Looks like I might manage a clean install after all.
Thanks to Saul - sorry I missed your leaving drink by the way - for this link that poijnts out that there is a way to perform a clean install even with an upgrade key. I am squeaky clean and have a licensed copy of XP (it came with the Dell) so I think I am allowed to give this a go. Pity it wasnt in the Quick Start Guide in the box. That guide must have been written for full and upgrade licenses as it describes doing a clean install, but that is not on offer to upgrade customers. Whoever did the OOB testing at MS should have their arse FIRED!
Christ, I have just read the FRONT of the box. It says - "For users running MS 2000 and XP and Vista only. Backup and clean install may be required. See back of box for details."
Damn right it was required, I just couldnt figure out how to do it.