If your a little handy buy a internal HD then an encloseure kit and build your own and save a few bucks. It's not that hard.
Seagate is a best HD right now, it has a 5 yr warr but if you buy any external HD you only get a 1 yr warr.
I recently built an external 7200 RPM, 120GB Seagate HD, with 8MB Cache, (You want at least 8 MB Cache, most ext HDs only give you 2 MB Cache, while some of the big HDs, 200-750GB, have a 16 MB Cache now) and with the enclosure kit it cost $85USD.
Got the internal HD at Best Buy with 5 yr warranty and the kit at
www.newegg.com.
Needed USB 2.0 ports and picked a PCI USB 2 card, with 5 ports, for $6 at Newegg to.
Total cost with shipping came to $92USD, a little cheaper than going with Tiger Direct.
It was all 'plug & play, turned it on, XP recognized & installed, it with no problems and its been running a couple months now.