Ok. Go here and download version 4.42. Install that, then go to your start menu. Because you have vista, it should be either this or this. Click "Default Programs" (at the top for the first one, near the bottom right on the second one.)
You should see this. Click the second link, "Associate a filetype of protocol with a program."
Scroll down to .zip as shown here. Click "change program". Then click browse. It should take you to program files, as shown here. If not, find your way there by going to c:/Program files . Then, find the folder called 7-Zip. Click it, then double click the file called 7zFM. Then click ok.
After all of that, try to open the file. It should work.