Why not try taking out the 80Gb HDD, change the 200Gb to a master and see if its recognised.
If it isn't seen send it back,
If it comes up as 137Gb, flash your bios,
If it comes up with an unknown size your mobo cannot cope with it.
XP is fine and will recognise it after the bios loads it.
I know as i had almost the exact same problem, I had a 120Gb Wester Dig in and bought the 200Gb about a year ago. But if I were you i'd swap both over to NTFS, Xp sometimes goes berserk with FAT32. It once deleted 90Gb of my data claiming it wasn't mine. And besides a good solid formatting of drives now and again is good for them.