How vulnerable is Linux in general from finger faults from normal everyday Windows users?
From my experience, I would say that once you set up a Ubuntu box properly, normal users won't make it crash easily. My parents are not exactly technical people, and they have been using Linux distributions for years without larger problems (actually they got a Fedora box just now).
Ubuntu doesn't underestimate security. It was written with security in mind, unlike Windows. By default Ubuntu won't allow you to download or install any programs without some form of permissions.
You don't need anti virus software. It's also reliable and well written. Everything Windows can do Linux can do as well.
Try it out! Choose try Ubuntu once you download it , and create either a bootable CD/DVD or USB drive. See image below to see if Ubuntu is for you.
I believe Ubuntu is making great progress in making its software more user friendly and easier to use.
Part of the info compliments of Squidoo
I think Windows is much more problematic with "finger faults" but of course it's easier to handle because most applications are written for windows. And it's easier to install any other software. If you want to play the administrator and help them to configure everything , Ubuntu is a good Idea. If they are interested in learning something new!
Have you thought about a dual boot system ? So they can switch back if necessary.