windows xp install on external HD

K i read the otherpost about installing win xp pro onto a external HD, but i found this article.... http://www.ehow.com/how_4814278_install-windows-external-hard-drive.html
and was wondering if this sounded legit? I am currently trying to install xp pro onto a external HD, and I am getiing a error message saying I dont have proper permission or some thing.(should have taken a picture). Friends HD crashed, and we are trying to use his external HD as primary drive. I've already defragged, and partitioned it so he wouldn't lose his info. Any tips? Thanks

 

This isn't what your asking about but if his HD isn't fried, you could boot a live CD such as Knoppix and copy his files across a network to another computer or a usb drive, Reinstall XP on his computer and copy the data back.