Something you should consider is that the 7200.11 drivers are generally faster than the 74 and 150 gb raptors. The 640GB one from Western Digital is a very good choice, model name is WD6400AAKS. It's cheap and huge too, only a bit slower than the 300gb velociraptor, faster than the older ones.
RAID 0 does fail often though, and provides absolutely no gains in gaming. I'd advise against it unless you absolutely need the little extra speed.