I recently had to do a wee bit of hard drive replacement surgery on my venerable powerbook g4 400MHz which has served me well for quite some time. Unfortunatly, the 10G drive that it came with has been filled with various amounts of junk almost since I had the thing installed... originally I had left OS 9 on the thing, but as I almost exclusively use Debian these days, my original partitioning scheme was leaving me with little choice but to completely replace the drive.
I settled on a 30G Hitachi drive (used to be IBM) which I had shipped to me along with a FW enclosure so I could easily dd the data back and forth from the current drive to the it's replacement. Unfortunatly, it took a bit for the FW enclosure to get drop shipped from whoever made the silly thing, and so I was sitting staring at a nice 30G drive with no way to install it. The installation went pretty smoothly, and as I type this, the drive is purring away inside the laptop. It's way quieter than the previous drive (even though I thought the previous drive was really quiet compared to the others I've used previously.)