It's also important to think about how your going to partition those drives, especially if you plan to keep proper backups. If your interested here is my setup on my 2 drives:
Western Digital Raptor 74GB 10,000 RPMs *SATA
Partition 1: C:, 25GB, OS & Other Programs
Partition 2: E:, 33GB, All Data & Other Files
Partition 3: G:, 20GB, Games, Game Programs & other game related files
Western Digital 250GB 7200 RPMs *SATA
Partition 1: M:, 157GB, Media Drive (Music, Video, Imaging)
Partition 2: I:, 15GB, Image of C: (Clean Install w/primary programs installed)
Partition 3: D:, 25GB, Backup of C: (updated weekly)
Partition 4: F:, 33GB, Backup of E: (updated weekly)
Partition 5: H:, 20GB, Backup of G: (updated weekly)
I know it's prolly overkill but hey, I have never had an issue with data recovery with this setup. And on a side note, I use CDs to backup my media drive.