When I installed a second sata on my xp computer (if I remember right) It would show up in one place (my computer or device manager) but it was un-accessable. I had to go into it via properties page and tell xp what kind of drive I wanted it to be (removabe, etc). After that it worked flawlessly.
I pulled my hair out until I figured that out. I know that it would only show up in one place and the issue was simply assigning the function of the drive.
I thought the same thing, that it would not recognize it, but it knew it ws there and just would not give access to me.
You may poke around the seagate page or another manufacturer. try a search for xp won't rcognize sata drive.
F.S.