Thanks for all the answers chaps - I'll investigate the various options you've suggested.
The problem manifests itself when it is trying to download SP2 as an update - it stops with an error message saying there is a problem with the license, so I'm pretty sure it's a dodgy copy. When I was discussing this with my friend she said the guy who supplied the PC had told her not to do updates as they wouldn't work - she didn't realise the implication of tbis - so I'm pretty sure he knew what was going on.
Thanks again