Cannot Get Connection -- Could a firewall be blocking it?

[Hal Vaughan]

I've asked this before, in variations, and never gotten a response.  I always 
wondered if it was just low traffic on the list or what.  I figure this is a 
good time to re-ask it, since with all the discussion over quoting styles, 
there must be a lot of people reading the list now. 

I have a client who cannot connect to me using RealVNC (both client & server 
on Linux). B We've tried this from his office and his Father's office, nearby. B 
I'm running vncviewer:

vncviewer -listen

on my system, with my firewall set to forward port 5500 to my workstation, and 
it forwards port 80 to port 5500 on my workstation as well (I leave these 
ports closed unless I'm working with a client). B On his system he's running 
vncserver and it is using display :1, so he uses this command line:

vncconfig -display :1 -connect myname.dyndns.org

And we don't get any connection.  When I run the same line from inside my LAN, 
so it connects by going through dyndns.org, it works. B When my friend does it 
from his office, nothing happens and he gets no connection. B  I figured his 
firewall may be blocking outbound connections, so I had him try:

vncconfig -display :1 -connect myname.dyndns.org:80

to send the connection through port 80. B If he tries to read a web page on my 
address, I see it on my firewall logs, but when he tries this (trying to 
connect to my vncviewer), I see nothing in the firewall logs.

Is there any way to make the connection look like an HTTP connection (other 
than using port 80)?

Can anyone guess what is likely happening?  Is it likely his firewall is 
blocking the outgoing signal because it realizes it isn't an HTTP connection?

Thanks!

Hal