When I try to open any programs or files, other than the internet, I get the message -are you sure you want to add the information in c:\filename and path .... to the registry?
I cannot even load a virus checker program now because of this, any ideas!

Have you accidently changed the default handler for programs/files to regedit? Or ran a program which did this? ie; Right clicked and chose "Open With..." and "Always use this program to open this type of file" (or similar message).

This message usually only comes up when you click on a .reg file.

Ref:
http://support.microsoft.com/kb/310516/EN-US/