Click 'Configure' on the bottom of the Multiplayer page. Check all 3 boxes, and then restart N4.
Under 'Connect Via' click on the arrow and choose your connection IP. You may have 2 or 3 different IP's, try each IP until one works. The NASCAR Racing 4 'IP Address' is 126.96.36.199:33450.
Click 'Start', you should be in the server :).
The above applies for NASCAR Racing 4 and NASCAR Racing 2003. To the NR2003 racers, download the NASCAR Racing 2003 patch here:NASCAR Racing 2003 Patch Download The NR2003 IP address is posted on teamspeak an hour before each event.