Run Unix or Linux from an external hard drive

How to run Unix or Linux from an external hard drive?

i use linux, the cd's are called distro's... (distributions) theres dozens of em, all free and all slightly different...

if your new to this try linspire xp2007, its dead easy to use... set your PC to boot from the CD, and thats it...

looks like xp, behaves like XP but it doesnt crash... and all the associated software is free