Denied access

Hello,
I have been experimenting with items from the article:
http://www.microsoft.com/windowsxp/u...storeperf.mspx
When I try to disable startup items with the System configuration utility
I receive an access denied alert even though I am logged in as an admin.
How does one log in as an admin user if one is already logged in as the
admin user?

Thanks for any assistance