Admin Privileges All Messed Up

Hey Folks,
First time poster long time reader; just need a little bit of help.
I can't find this issue anywhere else and I hope I don't have to reinstall everything.
Running Snow leopard 10.6.1 on a 24" iMac
So I am logged into my account, the only account on the computer and subsequently the only account with "admin" under the name.
If I try to do something that requires a password I get a box that says
"Type an administrator's name and password to allow....."
If my memory serves me right it used to fill in the Name field and then require the password.
Both fields are blank and if I fill them in with the correct information is says
"You must type and administrator's name and password to make changes, try again"
Now I know I am entering the correct information and still nothing works.
Help?
I've tried inserting the install disk and running diskutility but that solved nothing.
Any clues?
Thanks
-austin

If you go into system preferences/accounts, is yours the only account there, with your pic, name, and admin under your name?
And if so, if you try to unlock it and type in your password, does it unlock?