+5  A: 

In Windows Vista, your account doesn't have the Administrator role unless you've elevated to that level through User Account Control.

My understanding is that you effectively have two user accounts -- one normal level, one administrator level -- with UAC mediating the switch between the two.

Bevan
Technically you have only one account. You initially get a restricted token, when you elevate, you get an elevated token.
1800 INFORMATION
I found out how to check whether user is in Admins role or not through a link in another StackOverflow post - http://tinyurl.com/ct5t2b which links to http://tinyurl.com/m5ukz
Sung Meister