Out of IP addresses

Hey all,

Have a network with all static ip addresses in the 192.168.0.X range. It was setup this way as there are 4 buildings each with their own routers for internet access but the buildings are connected via wireless bridges (WiLan units, all buildings are with a 1/2 mile of each other).

Soon I will be running out of IP addresses. How do I add additional computers once I run out of addresses to assign in the above range, and have them still be able to communicate with each other?

Any insight would be appreciated!