if you reinstall Vista to a new hard disk.
By the way, it's bad practice to have only one administrative account on a machine. It's a lot of work if it gets corrupted or you forget the password.
But I'm sure there are ways to circumvent this. Look at http://home.eunet.no/pnordahl/ntpasswd/ for example.
Need help! I lost my Windows vista admin password
I have lost my Windows vista administrative password and can't find it to save my life! Am I stuck having to wipe and reload my computer? Or is there a method I can use to reset it or bypass the log-in screen. I do not want to lose everything! Thanks for your time!