Bite the bullet, and get a bigger hard drive. You can save money by going for a fast (7200 rpm) but smaller (40 gig) drive or a slower (5400 rpm) but larger (100 gig or more) drive. Or jump into the 21st century with one of those killer special edition western digital monsters. 7200 rpm, quiet bearings, 8 meg buffer, capacities up to 200 gig if I recall correctly.
Most places that sell software ought to have drive duplicator utilities that will automate copying the old data onto the new drive.
I'd avoid a used drive like the plague and I'd avoid IBM drives like the plague delivered in a bowl of broken glass shards with anthrax sprinkled on top, so make sure you buy something new and reasonable quality.
Oh yes... Some 5400 rpm drives are noticeably quieter than some 7200 rpm drives, so that might affect your buying decision.
http://www.storagereview.com (or something like that) reviews drives.