The external CD drive would not boot from usb. Trying to install from the XP disc was not possible because the XP on the laptop had been upgraded to sp2 whereas the cd was earlier. If you copy the XP cd to your hard drive it will be the same as trying to install from the external drive and will detect possibly that the XP cd is earlier than the installed operating system. I subsequently found a supplier for the internal drive for my laptop. As I had already purchased an external CD writer I only had fitted (I could have done it myself, its a doddle) an ordinary cd drive @ £41.00 fitted. I was told by the shop I purchased it from that most laptop drives are the same and it's just the face plate that differs. I purchased mine from H F Systems in West Bromwich. They have a web site. Their No. is 0121 556 5821.
I have just recived a new laptop from my employer, that does boot from the usb. If yours is a late model it may also. The way to check is boot up with a memory stick in the usb port. Hope this helps. You can email me on
bcarter182@aol.com if you need any more info. Good luck