Booting your PC from a USB drive

Here are some links, if you want to find out how to boot your PC from a USB drive:

Windows

Fred Langa (From information week) offers a step-by-step and illustrated guide on how to boot XP from an ordinary USB drive.

WinUSB is a free tutorial which allows the user to run a complete Windows XP version on an USB device/stick. This tutorial is some kind of manual which you have to follow, in order to let your modified Windows XP run on your USB device.

Another Windows XP on a USB drive tutorial here. After completing this tutorial, your Windows XP install should directly boot off your USB-drive, and be fully upgradable, DirectX games will run, all apps i tested work like normal, speed is the same as with a real HDD (you need USB2 though) - so it is in fact a fine solution as far as i can see.

Linux

How to Run Linux on a USB Drive. We successfully installed a distribution of Damn Small Linux on a Lexar 512mb Secure Disk USB 2.0 Jump Drive and it worked quickly and flawlessly. There's no guarantee that every USB Drive will boot Linux using this method (for example, the new Imation 256mb Wristband Drives would not work properly), but we feel a vast majority will work fine.

Booting Linux off a USD drive. Here is how to use a small USB pen drive as the primary hard drive for Linux.