connecting from computer inside network to computer inside different network

[Will Stateczny]

Hello,
    Here's my situation.  On my customer's computer, which is behind a 
network, I've installed VNC Server.  On my computer, which is behind a 
different network, I've installed VNC Viewer.  I've forwarded port 5900 
on my firewall to my computer's network ip address.  I've turned on VNC 
Listener on my computer.  When my customer goes to "Add a new Client", 
it will ask for the name/address.  I am at a loss as to what to put in 
there.  I tried my internet IP address coming in to the firewall, then a 
colon, then 5900.  I also tried my website name, a colon, then 5900, but 
both connections failed.  Does anyone know the value I need to put in?

Will