As addy says, a free supported *Nix maybe the way to go.
Before anyone shoots me down or this turns into a flame war, for most users Linux can be very easy to use, I say most because there can be some tweaking needed to get some windows only apps running on unix and some hardware does not have open source code to allow drivers to be produiced. But most people should be fine if installed correctly. My mum was running Ubuntu with no problems for two years. I have lost count of the amount of times I had to support her or my Dads laptops (always on a sunday innit - wanna come round for sunday dinnner boris? Oh and while you'r here can you take a look at my laptop for me).
To avoid that she got ubuntu, no problems, no malware. All I did was rename the icons, and put them on her desktop.