How would you secure your Parents' PC?

StirlingArcher writes: I've always built/maintained my Parents' PC's, but as Mum has got older her PC seems to develop problems more readily. I would love to switch her to Linux, but she struggles with change and wants to stay with Vista and MS Office.

I've done the usual remove Admin rights, use a credible Internet Security package. Is there anything more dramatic that I could do, without changing the way she uses her PC or enforcing a new OS on her again?

One idea was to use a Linux OS and then run Vista in a VM, which auto-boots and creates a backup image every so often.

Thanks for any help!