Yea, I forgot that i have the code for authroizenet already written.
took about 2 hours to do

here it is
1st you create object then use SendRequest to actually send that request to
authorize

using System;

using System.Net;

using System.IO;

using System.Text;

using XoopsNet.BLL;

namespace XoopsNet.BLL.RetailStore

{

public class clsAuthorizeNet

{

string _sLogin;

string _sPassword;

bool _bTest;

string _sInterface;

string _sBFirst, _sBLast, _sBAddress1, _sBAddress2, _sBCity, _sBState,
_sBZip, _sBCountry, _sBPhone;

string _sShFirst, _sShLast, _sShAddress1, _sShAddress2, _sShCity, _sShState,
_sShZip, _sShCountry;

string _sCustId, _sCustomersIp;

string _sInvoiceNum, _sDescription, _sCardNum, _sCardCode;

decimal _fAmount;

int _iExpMonth, _iExpYear;

System.Text.StringBuilder _bld;

public enum TRANS_TYPE { AUTH_CAPTURE, AUTH_ONLY, CAPTURE_ONLY, CREDIT,
VOID, PRIOR_AUTH_CAPTURE};

public clsAuthorizeNet(

string sBFirst,

string sBLast,

string sBAddress1,

string sBAddress2,

string sBCity,

string sBState,

string sBZip,

string sBCountry,

string sBPhone,

string sShFirst,

string sShLast,

string sShAddress1,

string sShAddress2,

string sShCity,

string sShState,

string sShZip,

string sShCountry,

string sCustId,

string sCustomersIp,

string sInvoiceNum,

string sDescription,

string sCardNum,

string sCardCode,

decimal fAmount,

int iExpMonth,

int iExpYear)

{

_sLogin = clsGlobal._sAuthorizeLogin;

_sPassword = clsGlobal._sAuthorizePassword;

_sInterface = clsGlobal._sAuthorizeInterface;

_bTest = clsGlobal._bAuthorizeTest;

_sBFirst = sBFirst;

_sBLast = sBLast;

_sBAddress1 = sBAddress1 ;

_sBAddress2 = sBAddress2 ;

_sBCity = sBCity ;

_sBState = sBState ;

_sBZip = sBZip ;

_sBCountry = sBCountry;

_sBPhone = sBPhone;

_sShFirst = sShFirst ;

_sShLast = sShLast;

_sShAddress1 = sShAddress1 ;

_sShAddress2 = sShAddress2 ;

_sShCity = sShCity ;

_sShState = sShState ;

_sShZip = sShZip;

_sShCountry = sShCountry;

_sCustId = sCustId;

_sCustomersIp = sCustomersIp;

_sInvoiceNum = sInvoiceNum ;

_sDescription = sDescription ;

_sCardNum = sCardNum ;

_sCardCode = sCardCode ;

_fAmount = fAmount;

_iExpMonth = iExpMonth;

_iExpYear = iExpYear ;

}

public void AppendPair(string sName, string sValue, int iMaxLen)

{

if( sValue.Length > iMaxLen)

sValue = sValue.Substring(0,iMaxLen -1 );

if( _bld.Length != 0 )

_bld.Append('&');

_bld.Append(sName);

_bld.Append("=");

_bld.Append(sValue);

}

public void AppendPair(string sName, bool bValue)

{

if( bValue)

AppendPair(sName, "TRUE",5);

else

AppendPair(sName, "FALSE", 5);

}

public int SendRequest(TRANS_TYPE type, ref string sAutorizationCode, ref
string sTransactionId, out string sReasonText)

{

sReasonText = "";

string sTmp;

_bld = new System.Text.StringBuilder();

AppendPair("x_login", _sLogin, 20);

AppendPair("x_password", _sPassword, 20);

AppendPair("x_test_request", _bTest);

AppendPair("x_delim_data", true);

AppendPair("x_delim_char", ",", 1);

AppendPair("x_encap_char", "", 1);

AppendPair("x_delim_data", true);

AppendPair("x_version", "3.1", 3);

//Billing address

AppendPair("x_first_name", _sBFirst,50);

AppendPair("x_last_name", _sBLast,50);

sTmp = _sBAddress1 + " " + _sBAddress2;

sTmp = sTmp.Trim();

AppendPair("x_address", sTmp, 60);

AppendPair("x_city", _sBCity, 40);

AppendPair("x_state", _sBState, 40);

AppendPair("x_zip", _sBZip, 20);

AppendPair("x_country", _sBCountry, 60);

AppendPair("x_phone", _sBPhone, 60);

//Shipping address

AppendPair("x_ship_to_first_name", _sShFirst,50);

AppendPair("x_ship_to_last_name", _sShLast,50);

sTmp = _sShAddress1 + " " + _sShAddress2;

sTmp = sTmp.Trim();

AppendPair("x_ship_to_address", sTmp, 60);

AppendPair("x_ship_to_city", _sShCity, 40);

AppendPair("x_ship_to_state", _sShState, 40);

AppendPair("x_ship_to_zip", _sShZip, 20);

AppendPair("x_ship_to_country", _sShCountry, 60);

//transaction info

AppendPair("x_customer_ip", _sCustomersIp, 15);

AppendPair("x_cust_id", _sCustId, 20);

AppendPair("x_invoice_num", _sInvoiceNum, 20);

AppendPair("x_description", _sDescription, 255);

AppendPair("x_amount", _fAmount.ToString("0.00"), 15);

AppendPair("x_method", "CC", 2);

AppendPair("x_type", type.ToString(), 20);

if(( type == TRANS_TYPE.CREDIT ) || ( type == TRANS_TYPE.VOID) || (type ==
TRANS_TYPE.PRIOR_AUTH_CAPTURE ))

AppendPair("x_trans_id", sTransactionId, 10);

if( type == TRANS_TYPE.CAPTURE_ONLY)

AppendPair("x_auth_code", sAutorizationCode, 10);

AppendPair("x_card_num", _sCardNum, 22);

string sExpDate = _iExpMonth.ToString("00") + "/" +
_iExpYear.ToString("0000");

AppendPair("x_exp_date", sExpDate, 10);

AppendPair("x_card_code", _sCardCode, 4);

HttpWebRequest rq = null;

WebResponse response = null;

Stream st = null;

try

{

string sPostData = _bld.ToString();

rq = (HttpWebRequest) WebRequest.Create(_sInterface);

rq.Timeout = 1000*60; //1 minute timeout

rq.MaximumAutomaticRedirections=3;

rq.AllowAutoRedirect=true;

rq.KeepAlive = false;

rq.ContentType = "application/x-www-form-urlencoded";

rq.ContentLength = sPostData.Length;

rq.Method = "POST";

byte [] byte1 = System.Text.ASCIIEncoding.ASCII.GetBytes(sPostData);

st = rq.GetRequestStream();

st.Write(byte1, 0, byte1.Length);

st.Close();

st = null;

response = rq.GetResponse();

st = response.GetResponseStream();

byte [] buf = new byte[3000];

int iIndex = 0, iRead;

while(true)

{

iRead = st.Read(buf, iIndex, 3000 - iIndex);

iIndex += iRead;

if( iRead == 0 )

break;

}

st.Read(buf, 0, 1000);

st.Close();

st = null;

string sResponse = System.Text.ASCIIEncoding.ASCII.GetString(buf);

string [] sR = sResponse.Split(',');

//sR[2] will be '1' if success.

string sCode = sR[2];

sReasonText = sR[3];

sAutorizationCode = sR[4];

string sAvsMatch = sR[5];

string sCvvMatch = "P";

if( sR.Length > 39 )

sCvvMatch = sR[38];

sTransactionId = sR[6];

switch (sAvsMatch)

{

case "A":

sReasonText += "<br>AVS: Street Matched, Zip does not";

break;

case "B":

sReasonText += "<br>AVS: No Info";

break;

case "E":

sReasonText += "<br>AVS: AVS Error";

break;

case "G":

sReasonText += "<br>AVS: Non-US card";

break;

case "N":

sReasonText += "<br>AVS: No Match on Address (Street) or ZIP";

break;

case "P":

sReasonText += "<br>AVS: AVS not applicable for this transaction";

break;

case "R":

sReasonText += "<br>AVS: Retry - System unavailable or timed out";

break;

case "S":

sReasonText += "<br>AVS: Service not supported by issuer";

break;

case "U":

sReasonText += "<br>AVS: Address information is unavailable";

break;

case "W":

sReasonText += "<br>AVS: 9 digit ZIP matches, Address (Street) does not";

break;

case "X":

sReasonText += "<br>AVS: Address (Street) and 9 digit ZIP match";

break;

case "Y":

sReasonText += "<br>AVS: Address (Street) and 5 digit ZIP match";

break;

case "Z":

sReasonText += "<br>AVS: 5 digit ZIP matches, Address (Street) does not";

break;

default:

sReasonText += "<br>AVS: code - " + sAvsMatch;

break;

}

switch (sCvvMatch)

{

case "M":

sReasonText += "<br>CVV:Match";

break;

case "N":

sReasonText += "<br>CVV:No Match";

break;

case "P":

sReasonText += "<br>CVV:Not Processed";

break;

case "S":

sReasonText += "<br>CVV:Should have been present";

break;

case "U":

sReasonText += "<br>CVV:Issuer unable to process request";

break;

default:

sReasonText += "<br>CVV: code - " + sCvvMatch;

break;

}

int iErrCode = Int32.Parse(sCode);

//SaveCCTransactionHistory(type, Int32.Parse(_sInvoiceNum), iErrCode,
sReasonText, _fAmount, _sCardNum, _sCardCode, sExpDate);

return Int32.Parse(sCode);

}

catch(Exception e)

{

//clsGlobal.SendEmail(......);

return 0;

}

finally

{

if( response != null )

response.Close();

if( st != null )

st.Close();

}

}

public string GetError( int iReasonSubcode)

{

string sError = "";

switch( iReasonSubcode )

{

case 4:

case 5:

case 6:

sError = "The credit card number is invalid";

break;

case 7:

sError = "The credit card expiration date is invalid";

break;

case 8:

sError = "The credit card expiration date is invalid";

break;

case 11:

sError = "Duplicate transaction has been submitted. Please wait 2 minutes
before resubmit";

break;

case 37:

sError = "The credit card number is invalid";

break;

case 78:

sError = "The CVV code is invalid";

break;

default:

sError = "";//"Transaction declined - " + iReasonSubcode.ToString();

break;

}

return sError;

}

}

}