Whoa, hold the screwdriver! You don't need to do all that. Download, burn and boot from a Ubuntu Linux LiveCD and boom, you're on a Linux machine. No cracking the case open or purchase of a usb case enclosure required.
Choose the first option to run Ubuntu without installing (or some wording like that...) Once the shell comes up you can access the hard drive through the Places menu, plug in your usb key and copy over your important files. When you're done, right click the usb drive icon on your desktop and choose Unmount, Eject or Safely Remove (doesn't matter which) before you remove the usb key to make sure its done copying files.
Hardest part of the whole operation is figuring out how to burn an iso CD image if you're running Windows XP.
No need to burn a CD. Just download a utility called "unetbootin" (google it). Download your ISO image then run unetbootin and have it place the image on a $5 flash drive. You could do this with any of the regular linux live CD images or the linuxrescuecd. Works like a champ.
bump for later use...