Step 1 - Locate file
Step 2 - Right Click the file -> 'Rename'
Step 3 - Amend '.zip' to the end of the file and hit enter. Alternatively you could try locating and opening the file with any file compression tool such as Winzip, winrar, winace etc.
Step 4 - Open zipped folder and view contents, it will be located under quickviwer .
Cannot see the 'zip' extension??
You need to enable file extensions for known files. In Windows Explorer (where the file is) go to tools (in Win Vista and Win 7 hit 'Alt' to bring up menu) then go to 'view' and untick "hide extensions for known files types". Remeber this location as you will need to tick this option back to how it was otherwise you may mistakenly rename a file you have no idea what the extension was.