I dont know if this is a hardware or software so i posing here. i got a new hard drive and i removed (plug out IDE cable and power cable) the old hard drive, installed xp on the new one. so i plug back in the old hard drive and booted up di pc. when i tried to get files from the old hard drive it keep asking me to format the hard drive. why does this happen and what is the solution?

I honestly dont see why the old drive wouldn't work. Your saying you have the new installed drive in and yu have the old drive connected to anothe ride cable using it as a slave just to get data from etc... and its saying it needs to be fomatted?? you could probably try an enclosure to see if the same problem occurs. If it does then it might really be the drive. Also you could try putting the old drive back in and see if it boots with the old install of xp.

i need to try that. do i need that jumper thing to set it to master or slave? cuz i dont have 1

it would be good to have some idea what drive is master and what is slave..... If u are using cable select u need to make sure you are using a proper cable that supports CS.
I think the safest thign to do is set it manually make the Window drive the master... u should have soem small jumpers on some old piece of equipment u have laying around there.

Yeh, get jumpers d00d it could be your problem.