I would love to help you here, but it seems that this thread is getting into the realm of illegal copyrighted infringment material.
However if one was wishing do such a thing, (which you deffinatly mussent, or anyone else for that matter) you would download a bit torrent client, such as azureus and install it (just google it), then you would go to a bittorrent website, such as torrentspy, or thepiratebay, and search for windows xp and download the file. Once the torrent loads into the bit torrent client (azureus) and finishes some time later, it will likely be in the format of an image file, (iso, img, etc.). You would then need a cd burning program that can burn cd images, such as nero 7, and you would burn the image to the disk. (Again research on google if you have more questions into this). After it is burned you have a completly real (or as real as it gets) windows xp cd (you already have the cd key but it is not needed for your application) to do what the directions state for repairing the master boot record.