I've noticed that you can't get back to the install page (where we discuss system requirements) after installing - we'll look into that!
Photosynth runs on Windows XP SP2 and SP3, and Vista, and requires IE7 or Firefox 2 or 3. There are a variety of video cards out there and we haven't tested them all, but the general requirement is that you have a minimum of 32mb of video RAM, with 64MB or more recommended. DirectX7 is recommended. You should have at least 1gb of system RAM and a 2.0GHz CPU to get the most out of Photosynth. You'll also need a broadband network connection. On the Mac, Bootcamp will work, but not Parallels.