well....you can always go into a computers settings and get a round the password....(thru dos/safe mode or when its just starting up)
my advice to you is to just delete erything he downloaded
tell him to put it on a cd......b/cuz you are deleting it....but its almost impossible to keep sum1 who knows what they are doing out of your pc......unless some1 else knows the deal...but i dont...
best i could do.