How do I hack a windows vista pword?

I'm a standard user and I want to change my dads pword, hes an admin on my pc. i wanna change his pword so i can make myself an admin and no i cant download software cos i'll need the password but i can download software that is a winrar file so i can just extract it and use without the password and ive already tried run-cmd-net user, and whatever, and it comes up with access is denied so that dont work cos for it to work, you have to be an admin. if you know any other way for the run-cmd thing to work properly without being an admin, tht would realy help thanks!!!!!!! and also, ive tried mozilla firefox, options and saved passwords thing but it only works if you have saved the passwords, thanks!!!!!!!