Not sure if this would make sense but this is how I have it set up on my main box which is a Vista64 machine (boo hiss) 🙂 Anyway my setup is as follows which works for me.
Local Drives
-74GB 15K U320 SCSI drive (system, applications and PS scratch)
-36GB 15K U320 SCSI drive (system swap)
-120GB SATA (Games, work in progress)
-80GB SATA (System Images, temp space)
Network drives
-2x250GB SATA in network server for important data storage
-1x500GB SATA in network server as weekly backup of the 2 drives
Seems way overkill but stuff was cheap and plus I enjoy spreading the load amongst multiple spindles if I have to do video work while compressing files while in photoshop running some kind of batch convert then maybe jumping into a game while all that happens. I find when its off multiple disks, performance does not suffer at all.