Any way to create a user account who can install only for itself?

Windows doesn't provide this ability, but perhaps there's another way? Let me explain the situation:

I'm currently configuring a new PC with Windows 7 Home Premium for my father, to replace his old XP one. He is a simple user, using a limited selection of software and never installing anything. However, when his children and grandchildren visit, they often install games and software for their own use. He's okay with that, but he doesn't like when the result is a change in the computer's behaviour, such as changed association, extra bars on the screen, a multitude of icons on his desktop.

I will try using two accounts and human engineering (i.e., telling everyone not to install anything on his account). He will have a standard user account, and a "family" account will be administrator. Problem is, this is totally open to abuse, because an administrator account can install anything on any account, change account permissions, etc. This is a problem if people don't make an effort to behave.

So my question is, is there a way (via additional software is okay) to enforce this division? One way would be to disallow any installations on my father's account. Another, better, would be to allow the family account to install stuff, but not have that affect anything else.

Any ideas how to achieve this?

Thanks!

The only way is as MilesAhead has suggested. All admin accounts are equal and you cannot restrict what they can do. This is a basic concept of Windows security.