Ok, if you have your XP key, you can download any XP cd from the web and use your key with it. With that CD you can do a recover of your OS.
Where do I go to download this? I have my key.
From any torrent web site. Just make you sure that the version that you download is the same that the key that you have. For example, if you key is a Professional edition key, you need download a XP professional edition.