John,
First of all find out which Windows version are you running: click on the Windows button (bottom left of screen) and in the box where you can enter a programme name type:
dxdiag
.... and hit enter. If it asks about checking for WHQL digital signatures just say no (it causes unnecessary delay for what we are doing). A panel opens and you should see:
Operating System: Windows...(and this states the version you are running)
Delete all your previous '7-zip' downloads. If you click on Windows... Computer (windows Vista or Windows 7) or if you go to the Desktop and open My Computer (Windows XP) you should see your Downloads folder. The downloads should be in there. Also see if anything else downloaded when you thought you were downloading 7-zip because some download sites fool you into clicking the wrong download button. Delete that too and check to see if that wrong programme uninstalling (you may have accidentally installed it thinking it was 7-zip.
OK now we should be clean.
Download the 32 or 64 bit version according to your operating system from Jokerman's link:
http://www.7-zip.org/
When downloaded all you need to do is double click on the filename and it will install. Just agree to any terms, conditions etc.
After that you should find you can right-click on the patch file (.zip or .rar) and the menu should list 7-zip. Left click on 7-zip, Left click on "Extract Files..." and then navigate to your game folder in the file panel that opens. Then Click OK and the patch should install to CoD.
Good luck
