Now for multiple hard drives, I'm not sure. There are a couple of guys here that are far more knowledgeable--they can probably give you more advice than I can...
(All my experience has been with one hard drive...)
I'm only running with one drive; mybackup is in a pullout carrier and I never boot to XP with that drive installed in the bay.
Not hard. My work machine a few years back had two hard drives. The C: drive (set in the BIOS as I recall) was the main and ran Win95. I added another drive, installed Red Hat Linux on it, and installed the LILO boot loader on C: with the option to choose which OS.
(I've also built machines with three or maybe four HDs.)