I can't install extensions in CS 5.1

I am trying to install the WebZap V1.0 extension but it is not working. This is what I have done so far:

1. I downloaded the Extension Manager for CS5 patch and tried to install it. The patch does not intall and I get the response, "Update is not applicable".
2. So I tried to reinstall the WebZap extension and it fails.
3. I then download the CS5.5 patch and try to install it. The installation works and I'm told my Extension Manager is updated.
4. So I try to install the WebZap extension again and it fails. The extension manger "unexpectedly quits" and I am given a "Problem Report for Extension Manager".

All the instructions I found online say to do exactly what I listed above; install the patch then install the extension. Unfortunately it is not working for me. So am I doing something wrong or did I missunderstand the process or the steps?