One way to do it is to split your computer into 2.
Make your hard disk into multi partitions. Load the operating
system into each partition so that when you boot up, you can choose
which one to boot. Choose "clean install" the 2nd one and 3rd one.
You can load 2000 in one, xp in the other and Vista in the
third.
Setup one of the OS so that he cannot log in. Let him do what he
likes with his own.
The rest like what about activation... how to partition... ask the
rest here...
