this is so cool! I was trying to get the mi-Ugens running on Windows for the last 2 days or so without success (struggled with my C++ compiler and stuff), so it's really great to have this easy option now!
In the mi-UGens-Windows.zip the "Classes" and "HelpSource" folders are empty. Apparently though, one can just take those from the mi-UGens-Linux.zip
Works like a charm! (from what I've tried)