Disk replacement for the H100 series is easy enough. Just remove the top and bottom covers (you need a Torx T8 for this), remove the back plate, and the HDD is right underneath the battery.
You can clone your old disk's contents to your new drive, swap disks, and close it back up.
I believe the disk needs to be a 50-pin ATA connection, and the tosh MK8007GAH looks like a likely replacement?
That one, AFAIK, is a good replacement drive. Plus, it's 80GB... double the capacity of the stock drive!

CompactFlash cards with a 50-pin ATA adapter card are also a popular choice for HDD replacements in these devices.