Have you considered a complete reinstall of Vista using your recovery disc? You may just have a buggy install.
As for antivirus, this is a common misconception that Vista comes with a bad antivirus. Vista does not include antivirus and you should use a seperate AV program - like Avast, which is free to home users.
Tip: easy way to find apps - click start and type the program into the search bar, you only need the first few letters, then press enter if its top of the search list, it will open it.
My stupid blog - www.spritesandbites.net