You can't use SATA drives.
For an internal drive, you can use up to a 120GB ATA drive. It doesn't matter whether it's ATA/100 or 133. For an internal drive, buy a Seagate. They give 5 year warranties on all their internal drives, where WD gives 3, and the others give 1 year only.
For a complete external drive, any FireWire 400 drive is gonna be OK, so also look at warranty duration. ClubMac's house brand, GVP, has drives in glossy white enclosures, you may want to take a look at those.
If you plan to build your own external drive, I'd again advise to go with a Seagate drive because of the long warranty. Choose a FireWire enclosure that supports "large drives" ("48-bit LBA"), so that if you choose in the future to put in a larger drive, anything over 120GB, you can.
tooki