What are the elements of creating a wireless connection between two buildings?

To create a point-to-point wireless links between these two buildings, you'll need a pair of wireless bridges, connected by outdoor directional antennas. Two examples recently written up on searchMobileComputing are Cisco's Aironet 1400 Series Wireless Bridge and Zyzel's ZyAIR B-3000 Bridge/Repeater. You can also find a list of wireless bridge products at Wi-Fi Planet, along with a short tutorial on wireless bridges.

The components that you'll need to purchase for each building include workgroup bridges (one operating in root mode and the other in non-root mode), outdoor directional antennas (e.g., Yagis), mounts for your antennas, lightening arrestors, RF cable, and RF connectors. To learn more about antennas and accessories, check out Cisco's Antenna Reference Guide. You may also want to look at "turnkey" bridging kits like the Proxim Tsunami QuickBridge.

You also need to consider network topology. Wireless routers like your Linksys WRT54G let hosts on a LAN to share one Internet connection through Network Address Translation. You will be using wireless to drop your entire remote LAN "behind" the WRT54G, making those hosts part of the Linksys LAN. You will therefore need to configure both of your routers so that traffic gets relayed across the wireless bridge to and from the remote LAN.

For example, suppose your Linksys LAN is 192.168.1.x and your Netgear LAN is 192.168.2.x. The wireless-facing interface on your Netgear must be assigned an IP address from the 192.168.1.x subnet, using the Linksys LAN-facing IP address as a default route. The Linksys router must be configured with a static route to reach 192.168.2.0 / 255.255.255.0 through the wireless-facing IP address of the Netgear. If your Netgear router is performing NAT, hosts on the Linksys LAN won't be able to send traffic to hosts on the Netgear LAN without further "server" configuration on the Netgear.