"XP" doesn't support over 127GB drives and such will not show. Maybe you had XP SP3 but didn't tell. That doesn't matter as I have to take your word here and use that for clues.
Also there is not much else in your post to use for clues. If you want other ideas, tell more.
I had an IDE hard drive in one pc, I wanted to move it from this one to another. Did that it didn't come up in windows explorer. Had a look in disk management and it was sitting there without a drive letter, it said unknown disk type, not initialized and unallocated. Now I have some very important things on this drive I need. I asked a friend what to do, he said take it back to the original pc and back it up. Did that, it comes up with the same thing. Both pc's are XP, I haven't changed it from being the slave drive and there is a master in both pc's. Can someone help me?