When you install some compression programs, like WinRAR, or Zip Genius, or a hundred other programs, they usually like to change the .zip file association, so that when you click a .zip file, it opens their program instead of the default Explorer view.

I had that happen to me, and it's very hard to change back.  If you do the normal "Properties ... Change Program", there is nothing listed there for "Compression" or anything that would indicate the default .zip view.

After some searching on the web, I came across a command that did the trick.  To run the command, first open a command window.  In Vista, it needs to be a command window with Administrator rights, so right-click the icon for the command window, and choose "Run as administrator".

Then, type the following command and press Enter:

cmd /c assoc .zip=CompressedFolder

Voilà!  Everything should be set to the default in an instant.