I bought a stock Hitachi 20GB laptop drive about a year ago, and it works just fine with the stock cable. Any ATA laptop drive should work fine. There are, however, a few gotchas:
1) Modern laptop drives have different mounting holes than older ones. So, you may have to drill some new holes in the bracket. I replaced an 85MB Maxtor, and had to drill 4 new holes. The good news is that the new drive is MUCH slimmer than the old one, so mounting was very easy.
2) Edit: InTheSand covers the partition sizes.
3) AmigaOS will sometimes run out of memory if you have large partitions or too many of them. I got TONS of Gurus after putting in my new drive, and had to tweak my startup-sequence for a few hours to fix it. Of course, my 1200 has only 4MB of fast RAM. I can't add any more RAM with the expansion card I have since it would conflict with my Compact Flash adapter, which is what I use to make backups.
