SNELL2000, 2005 & 2010 are all currently approved, as is BS6658-A F/R. The current Blue Book warns that SNELL2000 and BS6658-A F/R may be withdrawn, after the 2014 season and the 2015 season respectively.
Nicked from a post on PH as I can never remember the correct codes As long as it's one of those you'll be fine, even if TDOs suddenly start getting very strict.
Bike helmets are designed for one impact then a slide, car helmets are designed for multiple impacts, plus theres the fire rating to be aware of (will be much lower/non existant in a bike helmet). I personally wouldn't risk it, you've only got one head after all.