XP Media Center 2002 -> Pro SP2 "upgrade"

In an emergency we recently purchased a computer at a local dealer. The system came with XP Media Center 2002 pre-installed and was put to use immediately instead of first installing our corporate version of XP Pro SP2. Since Media Center is not able to join a domain, we have tried to upgrade it to XP Pro SP2. However, none of our licensed CD keys work for an upgrade and we seem to be stuck with performing a clean installation :3angry1: . Since this machine is used for data acquisition on an instrument, we would like to avoid the downtime involved in re-installing and re-configuring all of the required software. Does anyone know of a way to perform this upgrade?

Thanks in advance...