connecting from one local network to a different local network

[Will Stateczny]

Hello,
    I've been searching the archives but haven't found what I was 
looking for.  I figured out most ways to connect two computers with VNC 
except for the following scenario (which will probably be the one I run 
into the most):

My computer is in a local network at my office which gets it's internet 
via a server.  At my customer's site is the same setup.  How do I get to 
my customer's computer using VNC?

Will