*insert generic disclaimer here*
Yes, this is a little shady, but it'll work for you in this specific situation (kind of like what Sypher
recommended, but this is easier).
You can use
this program to make a floppy or CD bootdisk, then you can restart your comp, boot from it, change the password of any account on your computer (in this case the admin), then log in and make the account
Just make sure you choose to blank the password instead of changing it to something else. Read the site for more info ^_^