Basically it consists of creating a profile for the other version to use and installing Firefox 3 to a different location. I modified the instructions a bit and installed FF3 as default and then installed FF2 (again) to an alternate location. I also set FF2 to use the newly created profile so I could transfer my bookmarks to FF3.
Also, once both are installed, use FF2 to be your “default browser” then use FF3 to reclaim “default” status so that your start menu browser is FF3.
http://www.shankrila.com/tech-stuff/how-to-run-firefox-2-and-firefox-3-simultaneously/
