And don't forget to "Press F6 to install third party scsi driver" when installing XP! The drivers are normally on the MB utilities CD, and need to be copied to floppy disk, and this inserted when you install XP....Just in case you didn't know, it took me bloody ages to figure this out first time
My MB is a Gigabyte 7N400Pro2 and I've got a sATA boot disk, plus three IDE disks, a DVD burner and DVD player all hooked in ok. As rustle says, make sure the boot order is set to SCSI - CD - FLOPPY - etc but not HDD 0 as the old disk may end up booting.
Cheers