How do I route XDMCP through my NAT?

[michaelsanford]

I L O V E XDMCP with XDarwin, it allows me to graphically manage my RedHat box without putting the 21 inch monitor on my lunch table ... er ... "desk".

I'm currently invoking it with XDarwin using:
/usr/X11R6/bin/X -once -terminate -query 192.168.0.12

I have XDMCP configured to "Listen on UDP port 177". However, when I nmap my RH9 box, port 177 isn't listed, but 6000 is, as "X11".

So, if I want to route XDMCP through my NAT (so I can log in using my iBook outside my LAN) what do I have to forward? I tried 177 but no luck.

Attached is a screenshot of one of the coolest things I've been able to do with Panther so far (XDMCP logging in with the Finder in the background).