Passwording partitions

Hey, so I have a computer running windows 7 here, with the operating system installed on a partition, along with some programs (Firefox, etc.)
I have two user accounts, one administrator, one user, and I want to allow the user account to install programs, but only to a certain partition, and if they try to install to the OS partition, to ask for my administrator password. I've had to wipe this two or three times because my family don't listen,. so blocking access is the only thing I can think of.