Even if you cannot get a hold of reinstall discs from your pc's manufacturer, you should still have a Windows XP product key. Have a look on your machine for a sticker with this information. If you cannot find this, I believe it is possible to download a tool to get display the product key.
If you have a valid XP product key, you should see if you can borrow an XP install disc from a friend or something. It is perfectly legal for you to do this as long as you use your own product key to activate it.
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