There could be some sort of clash with shell extensions, the right click stuff. There is a tool called Shell Explorer View and that can show what shell extensions are loaded. Check it out,
http://www.nirsoft.net/utils/shexview.html, there is a download link at the bottom of the page and there is a 64bit version, so hopefully it will work with windows 7.
I don't know if this will work in windows 7, essentially you can check what is in your shell extensions (you should see a list of them when you right click) but this should be better as the right click menu changes depending on where it is that you use it.
So you can first look at some of those listed in the right click menu (when it freezes) and look for things that you added to the context menu and disable non-essential ones one at a time trying to find the conflict. This isn't quick or easy task, look for Context Menu entries in the ShellExView program and see what it turns up.
Other than that I'm at a bit of a loss, but it does seem to be a conflict in this area. I have had this happen some time ago, whilst it didn't happen every time it was enough to make me go hunting. It took ages (months) of internet searching when it got to be a pain again, eventually I found the culprit, something I didn't think would ever be an issue, my screen capture software SnagIt had a right click function, once removed never happened again.
Be very careful not to disable any Windows Shell entries.