Booting XP from a USB HD.

Factual Questions
1

I have a computer with Vista on it. And a 200GB external hard disk.

To save having to partition my Vista disk I thought about putting XP on the external and simply plug it in when I want to run XP, and unplug it when I want to run Vista (OBviously I would set it as the second drive afer the DVD in the boot sequence)

Is it possible to install an OS on an external drive?

2

It’s tricky and you’ll end up with certain disadvantages but I’ve done it a couple of times.

  1. You’ll have to edit some USB .inf files on the install CD.
  2. You won’t be able to have a pagefile on the USB disk.
  3. If you ever update your USB drivers, you’ll have to go back and edit them again.
  4. Your BIOS must support booting from USB.

The instructions are out there though. Try here.

I’ve never gotten Vista to work from a USB disk at all.