installing windows xp on external hard drive

[Jpierce]

How can I installe Windows xp Pro on my external hard drive.
My External drive is hooked up to the computer via USB, I would ultimatly like
to be able to run my windows and software from my external drive on anthother computer, In other words running windows on my external drive and not the main computers drive.
Can this be done? and How much would speed be a factor?

 

[Praetor]

1. The speed would be painfully slow
2. The ability to do so depends on whether or not the target machine is able to boot off the USB drive