I've run ide drives with long cables just sitting on my desk LOL. You should be able to crack the case of the PC open and plug it in to a free port, XP may see it as an unrecognized drive, just tell it to reinit the drive (NOT FORMAT) and you'll be good to go.
On the flip side, if your new pc has a manufacturer warranty, you shouldn't open up the case - that will void the warranty. In that case, your best option is an enclosure as mentioned above.
Good luck!