HOW TO LOAD WINXP ON AN EXTERNAL USB HARDDISK

CAN ANYBODY TELL ME HOW TO LAOD WIN XP/2000 ON TO AN EXTERNAL USB HARDDISK.
I HAVE LAPTOP WITH XP LOADED WHICH IS GIVING ME PROBLEMS OF NOT DETECTING THE HARDDISK WHILE BOOTING. SO I HAVE PURCHASED A 80 GB SEAGATE LAPTOP HDD WITH A SLEEK USB HDD-CASE. NOW I WANT TO MAKE IT BOOTABLE SO THAT I AM NOT IN A TOUBLE AT EMERGENCY WORKS.
CAN ANY BODY HELP ME

RASHID