I have been trying to get X11 forwarding to pass through a Mac. I have it working on one so I know it can be done. I discovered that if you set the DISPLAY variable with a .bashrc fragment like this...
if [ `ps -awwwux|grep X11.app |grep -vc grep` -gt 0 ]; then
export DISPLAY=":0.0"
fi
...then X11 forwarding won't work because the .bashrc script overwrites the DISPLAY variable. So I had to add an if statement like this (in my ~/.bashrc):
if [ -z "$DISPLAY" ]; then
if [ `ps -awwwux|grep X11.app |grep -vc grep` -gt 0 ]; then
export DISPLAY=":0.0"
fi
fi
[robg adds: I haven't tested this one.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050924195842936