I have just reinstalled xp, this went fine but it won't pick up my second hdd, it's in device manager as st2000dm 001-1CH164 SCSI device but not in disk management, it's a seagate 2tb.
If you are running xp I assume your system is a few years old so it is possible your computer will only support a certain amount of storage. You need to google the max storage for your motherboard and for your version of windows xp. If that turns out to be the case you can see if the manufacturer provides an update for your motherboard bios.