Was wondering if anyone has tried installing linux onto a external usb hard drive. Wanted to copy what mandrake has done with GlobeTrotter.

Though my system can't boot off a usb device, I would like this Linux installation to boot off from a CD and then continue loading off from the external hard drive. Have googled for this but all the results were cryptic and require that I make a linux installation for the external hard drive from a pre-existing Linux machine. Now I don't have Linux on my internal hard drives since I don't have any space to spare.

Does anyone have a hint as to how to do this?
I was thinking of doing this by using a cd-based Linux distro but I want I want to know if there are any alternatives.