theory will ask for the host/port of your MPD server
if you're upgrading from a previous version of theory, you might want to copy your theory.ini over from the old installation directory. Server info, Amazon AWS key, and saved streams are stored in that file. You should also consider copying the downloaded album art stored in theory-OLDVERSION/theory/public/img/art/ to avoid re-downloading all of those images.
IE and Safari are not currently supported since I don't have easy access to them for testing. All of my testing was completed on Firefox 3.5+ on Ubuntu Linux.
Windows users: theory does work on Windows, but it's more difficult to install. You have to use Python 2.5 since simplejson doesn't work on Python 2.6/Windows. Theory's installation and start/stop scripts do not work either. Read the installation procedure for Setuptools and Pylons on Windows and then start theory by opening a cmd prompt and from the theory directory type: \Python25\Scripts\paster serve server.ini I would happily add a .bat file to the distribution if someone writes one.