Does anybody make internal Firewire hard drives? I have a G4 450 DP, and I think it has an internal Firewire connector, but I have not seen any internal Firewire drives for sale.

There are no internal FireWire drives on the market. This is due to the fact that native FW drives don't exist. FW drives are only IDE/ATA drives in an enclosure using a IDE to FW bridge chip. You can put one of the portable drives inside the case, as long as you don't move it around, but if it's an external drive, just leave it external.

In later revisions of the G4, Apple removed the internal FW connection. It seems very unlikely that these drives will be made anywhere in the near future.