[K12OSN] VNC from "outside" the local network

[Jim Hays]

I have the following configuration for a K12LTSP lab in our middle school:

Lab Terminals <-------> K12LTSP server <--------->Rest of our 
network<------->Internet

The Lab Terminals are connected to the local side of the K12LTSP server 
and receive DHCP from K12LTSP (192,168.0.x) and the "Rest of our 
network" uses IP numbers in the 10.6.x.x range.

I need to be able to get a session (through VNC or X or ??) from the 
part of our network that is outside the K12LTSP lab. 

Could anyone tell me how I would go about doing that?  Now, when I try 
to VNC into the machine, it doesn't work. 

TIA