Administrator password on Vista

I have got a strange situation, I had three accounts on the computer one been the administrator. The problem is that someone changed that account to a normal account, now I can’t do anything because I don’t have administrator privileges. If I try to change anything it asks for the password, I didn’t use a password as administrator! Is this a default password? Or is there a way to make a new user with administrator privileges.
Thanks for any help.

User Accounts Password Recovery

Vista
Try Offline NT Password (Xp and Vista)

Try Ophcrack Live CD (For Vista)

Create a password reset disk in Vista (before you password protect your useraccount)

Read Microsoft policy about lost or forgotten passwords

Xp
How to log on to your Windows XP-based computer if you forget your password or if your password expires

Try Offline NT Password (Xp and Vista)

Try Ophcrack LiveCD (For Xp)


Edit:

Here's another one that many Users have reported as working
PC Login Now
Some screen shots H E R E