BleepingComputer.com: Help re: admin privileges

Hi, and thank you in advance for any help you can give me.

I am running Vista Home Premium, Service Pack 1.

1. Most recently I tried to run some online scans (HouseCall and BitDefender.) Housecall did not complete, and BitDefender says I don't have admin privileges. (I do. I thought. I am the only user on my pc, and I have two profiles--one with admin privileges and one without, which I usually use to surf the web.)
2. When I use HiJack, I am told my system denied write access to my hosts file, even after I followed the directions regarding deleting the host it showed originally. Since doing that, a hosts file shows up in the notepad, but not in the app where I can fix it. (Maybe it's actually okay; I don't know.)
3. I use CCleaner regularly; I have AVAST.

Again, thank you for your time. Let me know if you need any more information. I realize there are probably other things wrong, but this is what I have noticed.

I think you might run your browswer as admin in order to be able to complete those online scans successfully. Have you tried that yet?
Have you run HiJack This as admin?