Yes I'm beginning to think that's the only solution. I just wanted to avoid the hassle of having to find the right drivers for the chipset/audio/etc after Windows was installed (the Lenovo website lists alternative options for some of the hardware, so there will probably be some trial and error involved).Just wipe the drive and install the latest version of windows. It'll be near as fast as faffing about to reset admin password.
Sounds like you'd want to reinstall anyway, rather than use another person/company's OS install.
Where did you get the machine from?
Hopefully you're right. I'm just never confident that there won't be some funky piece of proprietary hardware that the standard Windows update doesn't properly handle. At the very least I'd expect to have to install chipset drivers manually, based on past experience.
It's a corporate desktop from a company that went under last year.