From the front page about 1097 not sure if it applies to the latest version or not, I'll see what I can find out.
Update from MS on 1097:
This build is NOT RC1, though as we approach RC1 we would like to use this build as a checkpoint to ensure that no new, major issues have been introduced.
Before you install: You should uninstall the previous service pack to return your system to Windows XP RTM then apply the new version. If you installed the slipstream version previously you will not be able to apply this update to your system. If you wish to test this build you will need to install retail Windows XP and apply the 1097 update.
Applying the standalone version of the service pack to an existing Windows XP machine does not require a new product key.
Thanks for that. I'm still using an early beta (1050). Not sure what the slipstream version is but Add or Remove Programs gives me the option to remove SP1 so I'd better do that. I'm not planning to install until the final version is released and I'll do a Ghost image beforehand to be on the safe side.