Since a lot of european keyboard do have important characters on their keyboard accessible with Opt- and Shift-Opt-modifier only, I did modify darwinKeyboard.c to honor this mappings. The solution to use xmodmap was not applicable for me, since I wanted to use XDMCP to connect to my session server. Any modifications to the Xsession would be wrong for my other X-terminals.
After I made these changes, I use Xdarwin for my daily work. Some keys still are not mapped correctly, for other keys, I did not find an X11 keysymbol.
Yesterday, i had to learn, that at least the german keymapping file /System/Library/Keyboards/Deutsch.keymapping does not contain the actual mappings used by MacOS X. :-(
I hope, somewon can test this patch with a non-german keyboard.