Installing windows and booting from external USB HDD

[sids]

I have a HP laptop and a AMD 2800 based desktop both running Windows XP Professional. I recently bought a 80 GB external usb Hard Disk. How do i make this hard disk bootable so that I can boot from it either on my home PC or my Laptop.

Thanks

Sids

[vinaypatel]

use bootmagic that provide option to boot PC from other hard disk ,but it is working fine for desktop i don't know abt Laptops