Live USB ala Linux Mint
 

Tasty. I've hijacked my wife's Vista Box with some user-friendly Linux. Followed these instructions and IT JUST WORKS! By the way, if you're considering Live USB but don't want Mint, you should check out pendrivelinux.com. All sorts of distros - great instructions. Cheers!

One distro that's not covered by pendrivelinux.com but is designed for booting with USB is Dreamlinux. I use Linux Mint KDE CE for most of my desktop work but for carrying around, I use the Dreamlinux on a pendrive -- its booting is much faster from a pendrive compared to the one I made from Mint (using instructions from pendrivelinux :))

unetbootin installs LinuxmMint to a USB now as well.