Same as ajp for me, extened music pack in menus but no music while racing (unless you count mum/girlfriend watching eastenders/corrie/big brother in the background)
When i'm in my car....well thats different, although music's not too loud so I can hear my V6 growl
If it is a short race, I just shut the music off and try to work my way up the grid (not like that happens alot of the time, because i'am very slow). If it is a long race, I usual just listen to anything.
I have my iPod plugged in to the computer with iTunes on shuffle. I voted rock since thats the closest genre to what I listen to, though most of what I have is probably considered metal.