Microsoft SQL Server uses port 1433 (TCP) and 1434 (UDP).
http://www.google.com/search?hl=en&q=ms+sql+server+ports+

Remember that depending upon what version of MS Sql Server is
installed, Remote connections may be disabled
There may also be other issues here so you may wish to view this
document
http://www.microsoft.com/sql/techinfo/administration/2000/security/winxpsp2faq.asp
that microsoft has prepared.

Hope this helps.

I forgot another method to facilitate debugging will be netstat -a -n.
This will list all applications that using ports. If you do a
netstat -a - n >netstatoutput.txt
netstatoutput.txt

this file should now open in notepad. Search for 1433 and 1434. If they
are listed then that will mean that the services are enabled and
listening. Also checking whatever firewalls are enabled. You should
probably make sure that the client does not have both SP2 ICF enabled
AND norton Firewall. If they do this may make troubleshooting very
difficult. both should have troubleshooting logs for troubleshooting
dropped connections.