Hi, I'm just bumping into this discussion. From what I read the reason you need such functionality is for a mozilla powerpoint plugin. Have you figured out how this embedding is done on Windows? I don't know much about it but I think embedding works using COM and perhaps almost the same as e.g. Flash.
For example codeweavers has a plugin to embed IE plugins in mozilla, the same for the KDE reaktivate project which did something similar for Konqueror (although it can be used on mozilla too as they put it all in a library). Likely IE plugins work differently but I think the same embedding mechanism could be used, so you won't need such an X11 hack. Regards, Roderick -- Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen! Ideal für Modem und ISDN: http://www.gmx.net/de/go/smartsurfer