How would you prevent other admins from accessing?

Yea so im using home premium vista and i need to know how i can block access to view write read exucute all files under my user name from another admin. and if your answer is right click properties security how do you actually use it becuase when i block the other admin i also get blocked. does it not work because he is a admin? or is it possible to download a 3rd party program that'll do the job? if so can you list em