It is possible, but not really recommended... if one OS screws up, there's a good chance that both will be hosed as a result and you'll have to reinstall everything again. It is MUCH better to dedicate one hard drive to a single OS.
As for being "Raptor-only"... you should get a large hard drive with a huge (32MB) cache... you won't notice a lot of difference in speed. (Not to mention you get a lot more space for the amount of money you'd waste on a Raptor)