It depends on how you copied the disc; a standard drag and drop of the CDs files wouldn't have done the trick I'm afraid, as the boot files on a CD aren't part of the useable file-structure of the disc. The only way it would have worked would be if you'd have made an image copy of your disc and then burned the image to CD.
There may be a work-around, however. Try searching for an XP boot image. You'll have to make another copy for it to work, but at least then you should be able to boot from it.