Linus: USER ERROR probably...
There should be a Tracks folder somewhere.. and the Track names appear in a box below the driver selection screen (12 tracks).
If not, try downloading it again
Jake: It's very simple: in the sound folder there are two subfolders. Default and Funny. You can change between the two soundscemes in the options menu.
To add a new soundscheme, just create a new subfolder! You need 5 soundfiles:
Damage.wav -> The sound you hear when you hit something
Ding.wav -> The countdown sound at the lights and the sound you hear when you start the final lap
Engine.wav -> The engine

Skid.wav -> Skid sound

Yeah.wav -> Sound played when the winner crosses the line and at the end of a season.
I just made a copy of the Default folder and replaced the sounds one by one 'till I found some I liked. Try this one to start with, that's the engine sound I'm using:
http://www.hi.is/~bjornkri/Engine.wav