Have you tried contacting Dell for a replacement XP CD?
Did you make an exact copy (Clone) of your HD to the external HD?
If so you may be able to use this (just an example) to transfer your external HD files to your new HD and the install the new HD in your lappy.
http://www.newegg.com/Product/Produc...%2FIDE+adapter
The ones listed at the beginning of the list.
You will need a working computer to do this.
Hope this helps.
Bill