Am I not the main user?

So sometiems when I try to change things on my computer it tells me that I can't do it. It says things like:
"You do not have enough access priveleges for this operation."

It's acting like I'm not the main user whereas I am and have been the only one to ever use this computer....

Any ideas? I run Windows XP....

 

What flavor of Windows are you running, Home or Pro?
Have you checked in you user accounts to see if you have administrator rights?

 

I've dealt with this problem many times in the past - I had this problem repeatedly on a machine upgraded from win 2000 to xp. This problem always seems to do with registry permission levels. I need to know exactly what you are trying to do when it gives this error, then I can help.

 

I'm on Windows XP Home edition. I checked my user name and I'm the only one there and I am the computer administrator. There's one other option as a guest but it's turned off.

I get the message when I try to make iTunes my default music player...

 

Well, a couple possibilities here.

You can change permissions on this key to full control for administrators:

HKEY_LOCAL_MACHINE\SOFTWARE\Apple Computer, Inc.\iTunes

Or you could change the value of iTunesDefault to 1 or 0, depending on what its set at. Of course, if you have to change permissions, it won't let ya