If your trying to RDP into the system, you have to make sure that in the firewall that either Remote Desktop or Remote Assistance is allowed through. Usually, I'm just able to go into system properties, click the remote tab and make sure that "Remote Desktop" is slected.
If your using Netmeeting, you have to make sure that Windows Netmeeting is allowed through the firewall. You also have to add the program C:\Windows\System32\mnmsrvc.exe is allowed through.