[OS X Emacs] Emacs make-frame-on-display not working

[pdfinn at uwm.edu]

Hello everyone,

I'm using Emacs 22.1 under Apple's X11, on Tiger; attempting to
connect to another computer running Tiger and Apple's X11.

(This is the first time I have tried to use the make-frame-on-display
feature, and am a bit foggy about X11 nuances.)  Emacs will make a frame
on my own XServer successfully, but attempting to make a frame on
another computer results in the complaint:

x-create-frame-with-faces: cannot connect to X server

The two machines have a working network connection; and I can display
XClients from one machine on the other's XServer via ssh---so I know
XForwarding is operational.

Emacs gives the same complaint with firewalls down, so it does not seem
to be a firewall issue either.  Machine address are specified in xhosts.

Does anyone have any ideas what I should look into next?

Thanks!
Peter