Hi Hakan

My Serial Port FAQ:

.NET 1.0/1.1 has no support for legacy ports (COM/LPT).

There are plans to add support for serial ports in a future version:
   http://groups.google.com/groups?&selm=O%23vQLn9bCHA.392%40tkmsftngp09
 "this sample is very similar to what we will be adding" :
   http://www.gotdotnet.com/community/usersamples/Default.aspx?query=SerialPort
    (note, project built with beta VS.NET, read gotdotnet comment)

  Future Directions for Visual C#
    http://msdn.microsoft.com/chats/vstudio/vstudio_032103.asp
     "We will add support for Serial ports to the framework..."

  Longhorn Preview with SerialPort class:
     http://longhorn.msdn.microsoft.com/lhsdk/ref/system.io.ports.aspx
     (should already be in Whidbey 2004)

With 1.0/1.1 you have to use PInvoke or Interop :

First understand the Win32 API as described here (C++):
  http://msdn.microsoft.com/library/en-us/dnfiles/html/msdn_serial.asp

MSDN article for .NET (mostly C#):
  http://msdn.microsoft.com/msdnmag/issues/02/10/NETSerialComm/

PInvoke samples for C#:
  http://www.gotdotnet.com/community/usersamples/Default.aspx?query=SerialPort
  http://msdn.microsoft.com/msdnmag/issues/02/10/NETSerialComm/
  http://www.gotdotnet.com/community/usersamples/Default.aspx?query=SerialStream
  http://www.gotdotnet.com/Community/UserSamples/Details.aspx?SampleGuid=5a96c071-
e9e8-47c4-bb9e-5413384f0c25

or for VB.NET:
  http://support.microsoft.com/?kbid=823179
  http://msdn.microsoft.com/library/en-us/dnvssamp/html/vbcs_usingthecomportinvbnet.asp
  http://www.gotdotnet.com/community/usersamples/Default.aspx?query=rs232
  http://www.mentalis.org/classlib/class.php?id=15
  http://www.corradocavalli.cjb.net/

or you can use the "Managed Extensions for C++" and write wrappers.
   http://msdn.microsoft.com/library/en-us/vcmex/html/vcconMCOverview.asp
   http://www.gotdotnet.com/team/cplusplus/
   http://msdn.microsoft.com/library/en-us/dncscol/html/csharp12192002.asp
   on your VS.NET path:
    ...\VC7\managedextensionsspec.doc
    ...\VC7\migration_guide.doc
  MC++ Sample:
   http://www.codeproject.com/managedcpp/howtocomport.asp

or reusing the VB6 MSComm ActiveX is easy, but it has some 'problems' (license)
  http://support.microsoft.com/?kbid=318597
  http://www.devhood.com/tutorials/tutorial_details.aspx?tutorial_id=320
  http://ourworld.compuserve.com/homepages/richard_grier/NETCommOCX.htm

commercial:
  http://www.sax.net/dotnet/communications/
      (Community edition in : http://msdn.microsoft.com/vbasic/vbrkit/)
  http://www.winsoft.sk/ncomport.htm

for the Compact Framework (Windows CE)
  http://www.microsoft.com/downloads/details.aspx?FamilyID=206645de-63ba-4e49-b9a3
-2d3b9cef4aa5
  http://ourworld.compuserve.com/homepages/richard_grier/CFSerial.htm

for Interop, use newsgroup:
  microsoft.public.dotnet.framework.interop