Yes, the Cordless gateway is a bridge between the wired network and the wireless network. It will do NAT for you, but I don't run it that way. I put it in a mode where it just bridges between the network segments, and as long as everything is in the same subnet all the devices will talk. I let my firewall/router handle NAT out to the Internet.
No, you can't use two of them to bridge two wired networks. However, there are now some 802.11b devices that will do that function. I know Linksys has one and I think I saw a D-Link the other day. They are in the $175 price range, but that is a LOT cheaper than wireless bridges used to be.
You could possibly have a Proxim Gateway in one location, and a remote PC with a PCI or USB adapter to talk to the Gateway, and let the OS on the remote PC route traffic to another wired adapter. When I tried it with Windows 2000 once it did not work properly, but I bet you could get it to work with Linux. But, you would have to put a gain antenna (and probably a directional antenna like a Yagi) on the remote adapter to be able to have a reasonable amount of separation between the gateway and the remote PC.