Problem in creating multiple admin accounts - Vista Ultimate 64 bi

I have Vista Ultimate 64 bit installed on my Dell Inspiron 1501 Laptop. I was
able to create one administrator account where as when I wished to create one
more administrator account, the "User Account" (from Control Panel) is not
allowing me to do this. I am able to select "Administrator" option during the
account creation process, after clicking "Create Account" button, when I go
back and check newly created account type, it is "Standard User"!! When I
tried changing it to "Admin" account type, the "Change Account Type" button
gets disabled as soon as I select "Administrator" option.

Help me how to resolve this. I want to create multiple administrator user
accounts in my vista ultimate 64 bit version.

Thanks.