Just to update, the sticker on the laptop is for XP home edition, and it states "label not to be sold separately" so I think it allows scope for me to give it a try.
I had no end of trouble trying to resurrect a tower with some 'dubious' installs and crawling with malware so I always think a fresh start rebuild by myself is the preferred option. If it does to tits up I'll just have to cross that hurdle later.
Cheers for now
Shaft