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.