BootCamp

I started off racing computer simulated racing leagues (online) about ten years ago with Sierra Papyrus' NASCAR Racing 2. Then went to NASCAR Racing 3, 4, 2002 Season and 2003 Season as they came out. Each subsequent sim offered better graphics, better physics, more immersive interface, better net-code, and more realistic rules/enforcement.
NASCAR, in their infinite wisdom sold rights to the NASCAR name to EA Sports in 2004 (I think it had a LOT to do with Dale Earnhardt's affiliation with EA and the enormous bid EA made for the exclusive rights to "everything NASCAR" for gaming). The subsequent NASCAR Racing sim EA came out with was horrible, and they provided ZERO support for their software issues. So we were still using Sierra Papyrus' NASCAR Racing 2003 Season until recently.
We're now using a sim called rFactor by ISI. This sim has a tremendous net-code for multiplayer online racing. It offers mods for nearly every type of racing - go-karts, indy racing, formula 1, grand prix, ....... you name it and there's a modification for it. The mods are free downloads and work seamlessly with rFactor's interface.
The league I run in now (Team RoadDog Racing) is beta-testing a mod called Stock Car Evolution. It's the newest incarnation of NASCAR Nextel Sprint Cup, which uses the 2008 Car of Tomorrow, all 30 2008 NASCAR sanctioned tracks, 2008 NASCAR rules, and some truly incredible online competition. The physics engines are amazing. We're still working with the programmers to get everything exactly right/accurate, but it's very close to a final release - version 1.00. NASCAR may have sold exclusive rights to their name, but that doesn't mean there's nothing better out there.

If you're interested, look up rFactor (by ISI) and Stock Car Evolution (under rfstockcars.com) and check them out.
Once you've competed online against REAL opponents, you'll NEVER go back to racing on a game console against artificial competitors again.