How do you log in as administrator on Windows Vista?

I began downloading TrendMicro (an anti-virus program), and it didn't finish
installing because there was another anti-virus program on my computer (CA
Internet Security - out of date). So when TrendMicro tried to remove it, a
message popped up saying that I didn't have the rights to uninstall the
program, and to try logging in as administrator. The Problem with that,
however, is that I don't have an administrator account. Reading other
messages on here, I've gotten the impression that an administrator account is
bulit-in. I use Windows Vista - it was on my computer already when I had
bought it, and when I first began using it just asked that I come up with a
username and password. So yeah, I've never been "administrator", just a
user...and therefore I have no clue as to how I log on as an administrator.

Hi Jussi.

Try remove the old Virus-protection with Add/Remove.
Thats controlpanel>Add/Remove.
You might be promted for the password by the UAC (User Access Control).
You are the administrator, but the program you install are not, that should
be why.

And then again - when you log on, Vista logs you on as standard user. Every
time you have to use admin-rights, the UAC will prompt you for password.

If you are a standard user, Vista will prompt you to elevate to an
Administrator by asking for the user name and password of an administrator
account.

If you are an Administrator, Vista will ask you if it's OK to elevate (and
won't ask for a user name or password).