Static User Thumbnails?

Hi. I’m using my wordpress blog sort of like a social networking site for a specific group of people. I’ve enabled ‘author’ access to all of my users so that they can post freely and comment – This was to take the place of the simplepress forum I had installed and then took away due to how excruciatingly laggy it made my website.

I was wondering if there is anyway to generate static user thumbnails so that my users gravatars will automatically appear in their posts without them having to take extra steps.