If you have it on your machine, a Firewire/USB 2.0 combo is a good one to go for. While you are at it, don't waste the effort with an 80GB unit. You will even fill a 250/300/400GB unit given time and the costs are disproportionate. the bigger the drive, the cheaper the Gigabyte cost.
Conan
PS search through this page and the one after - there is a thread there discussing Ext Hard Drives.