protect newbie users from themselves?

I have this friend/client, knows little about computers, every time theirs a problem (no matter what it is) he does a system restore...

his grandson was playing online games and something stopped working, so they did a system restore. lol. a week ago I got his PC working, got the spyware off, and he commented how fast it is (or was). now it's messed up again.

part of the problem, I think, is he has an admin account... so perhaps I should make him a standard user? Limit what he can do on the system?

thoughts? good idea or bad? I feel odd doing this, its his PC not mine... so I dunno. not sure.

Let me answer in this fashion. Every computer must have an administrator account. There is no need that everyone should use one everyday. I feel very confident in my computer knowledge and yet I use a standard account. Why?
After a hard day or maybe a problem day, I can do something, wrong without thinking. With a standard account, I will get a notice that will make me think.
So, let the inexperienced always use a standard account. For the very young or very inexperienced an account with parantel controls would be suggested or with Vista a limited account.
You say its his computer, tell him that either you paid for it or if he paid, does he want to pay to get it fixed?