Vista will run fine on a 24GB partition, which leaves you a fair amount of room for other applications.  I don't think games take up much more than 8GB each these days (don't have any newer games, so IDK).
Run 2x32GBs on RAID 0.  Over here, I can get an OCZ V2 30GB SSD for AU$139, so two of them will be AU$278.  A 300GB VelociRaptor costs AU$455 here, so the SSDs are a lot cheaper.
Plus, 64GB is enough for the OS plus your favourite games.  Store all your apps etc on the main HDD, not to mention the SSDs in RAID 0 will rape the VR any day :P