Hi Tim,
If you want to race in some or all of SP's year-long tournament series, pop along to this page on her website,
http://www.shadowprincess.com/Tourneys/MTM2.html
You'll find info there for online racing (general as well as tournaments) and can sign yourself up to the mailing list to be kept up to date with race start times and tracks etc. (Note we're on holidays for a few weeks at the moment - resuming in January.)
At present MTM2 online gaming is supported by BattleHQ and World Gaming Center sites, besides going there for arranged racing meetings for teams and tournaments, you can visit either and with luck at any time you'll meet people in the lobbies who'll give you a game.
http://www.wargamer.com/battleHQ/
http://wgcenter.com/
Shortlist to get started:
Make sure you have the MTM2 update patch installed (get it
here).
Then, sign up on one or both of the above sites and download and install their client software, and once you have that working you should be able to jump in
Then depending on the crowd you end up racing with you may download certain tracks to drive, etc.