Easy peasy. Will write it up when I get to work.
Here goes:
Download and burn the appropriate ISO of windows 7 and burn it to a dvd. You can find it here: http://www.mydigitallife.info/official-windows-7-sp1-iso-from-digital-river/ To the best of my knowledge this isnt illegal.
If the retail copy of windows does not accept the windows 7 upgrade key, you can download an XP iso here: http://www.microsoft.com/en-us/download/confirmation.aspx?id=25129 (this image is for XP pro)
If you are unfamiliar with burning images to a disk, download and install imgburn. Read through the installation window carefully as it tries to get you to install several other pieces of software that you c̶a̶n̶ should opt out of.
Worst case, Torrent an XP disk. I doubt anyone gives a shit about XP anymore.
IF all of this is too much to take in, id be glad to make you some disks and mail them to you or you can come pick them up.