You can't remove wininet.dll because it's needed by Windows to work properly. This virus is very sneaky, I have to say, as it replaces the Windows copy of wininet.dll.
I'm afraid that I have to re-direct you to another website for professional help.
http://forum.malwareremoval.com/By the way, did you update XP? As far as I know, users who have not updated XP will get this false positive from AVG.
If you've updated, please go to the forum and ask for professional help. I can't help more on this, and deleting the wrong files will result in reinstalling of XP.