On Windows 7 (64b Profi), when creating a GEM window, the contents aren't displayed. The window is created in the background, but it's always "invisible". The mouse pointer changes when going through it, though.
Tried it with both pd-ext 0.42.5 and 0.43.1-extended-20120504, so I guess the problem should be related with win7. Afaik, it works on xp with the same Pd versions.
Also tried with pd-van 0.43.2 and Gem-0.93.3-w32-i686.exe with the same results.