Wireless connection in the wilderness

I am attempting to use wireless to connect five different buildings to the Internet. Buildings are spaced 100 to 500 meters from the main office, with five or so PCs per building. Wiring is not an option because the ground is too rocky to lay cable, and there are too many trees to hang cable.

We tried putting a Linksys wireless router in bridge mode at each building, running wired network connections to the router from the local PCs, and using the router to bridge the distance to the main office. Whatever the cause, we could never get Internet access.

Do you have any ideas how this might be done?

Bridging building routers to the central office sounds like the right solution, but you'll need to boost the signal generated by each building's router. As you probably realize, link speed declines with distance. A router with factory-installed "rubber ducky" antennas can probably reach 100 meters in open space, but speed will drop drastically at that distance. Furthermore, your terrain is not open space -- those trees and rocks all absorb signal, reducing each router's effective reach.

To fix this, replace the building router antennas with high-gain directional antennas. Each directional antenna should be aimed towards the main office. If all buildings lie in one direction, replace the main office antenna as well. If there is not a reasonably clear line of sight between a building and main office, consider using a mast or building mount to position the antenna for better results, without having to reposition the router itself. If you are not already using the router's highest available transmit power, increase power as well. Use a wireless client at both ends to measure the opposite router's signal strength. If you are not able to achieve satisfactory signal strength/link speed with your existing routers, consider buying bridges intended for outdoor point to point links.

Given sufficient signal, configuring your routers to work together should not be difficult. Work on one problem at a time by taking a building router to the main office. Configure the main office router as a Wi-Fi AP and the building router as a Wi-Fi client. Get those devices talking to each other, and then relocate the building router where you actually need it. You didn't mention which router model you were using, but many Linksys routers do support bridging in this fashion. Consult your product manual for configuration details.