why are you going to run vista 64 bit??
you arent putting in more than 4 gigs of memory, and while most apps should work with 64 bit, do expect alot of issues and compatibility issues as opposed to 32 bit vista.
not sure i would run raid 5. i understand backing up your data, but why seperate it all then??
if your going to do raid 5, do it all or nothing. OS and all data, otherwise just do raid 0. or get rid of the 300 gig drives and pick up another 750 gig drive and do a raid 1+0. that way you end up with more space, and everything is still protected. or if you are looking for high performace, pick up some 10k rpm drives and a real raid controller card instead of using the onboard one.
otherwise it looks like a good build. to expensive for my tastes now adays, but if i was to drop that much cash, i would prolyl splurg a littl emore and do water cooling.. assuming you have enough room in your case.