Yup, I'd have to agree there, avoid Samsung like the plague for hard drives. They're generally fine for things like CD-Rom drives, memory etc., but I've had one die on me, plus several other peoples die when I was working at repairing the machines in Maplin. Maxtor are pretty good price/performance wise, and if it's not gonna be getting heavy use (and it's not), you should be fine. I've a Maxtor 80GB in mine that's on about 12-16 hours a day, but doesn't get heavy access, and it's fine 18 months later.
For backing up, I've a lot of stuff on mine, so what I do is use a 2nd hard drive (a 40GB IBM), and periodically copy everything across.
A thin drive shouldn't be too much hassle to fit in the 1200 case. It's been done for years and years, but again, if you don't fancy the hassle, find someone upgrading a laptop HD and throw them an offer for their old HD, or have a scour of EBay...