My company has 2 offices in 2 nearby buildings, the buildings are only about 20 or 30 meters apart, and each office has it's own working computer network (wired 10/100 with switch/hub). Because of some reason, the 2 buildings can't be connected via cable, meaning the only alternative is via wireless connection. Can anyone here tell me how to connect those 2 networks wirelessly? Is it possible to connect them using only 2 wireless LAN card installed in one of the computers in each networks? Converting every computers to wireless LAN is not an option because it will be too expensive.

Any comment or advice will be greatly appreciated.

Yes, you can do it (the hard way) with two WiFi-capable computers.

The more useful solution is to buy two wireless access points that support wireless bridging (or one access point and one bridge). Equip them with directional antennas and you are good to go.

You also might need a directional antenna depending on how good your wifi router is.

Also, if you want closer to network speed, look at the new non-standard MIMO routers. Almost network speed and better range than the older 802.11g routers.

What do u mean by "the hard way"? Surely 2 wireless Lan cards are cheaper than 2 wireless access point + directional antennas. The speed doesn't have to be very high, the data transfer isn't that big. Price is more of concern than speed here.

What worries me most is the reliability and security. Is nowadays wireless connection secure enough? I don't want someone hacking into our company's file server. And what about reliability? It isn't that far, but there is another building between the 2 office building, and the computers are located in closed rooms.

Thanks for ur advises

You will have two standard computers acting as routers/bridges instead of two dedicated boxes. I'd say it takes at least two days for anyone to set it up unless you have done it before.

Since price is an issue for you, then you will probably end up with two Windows-only wireless cards that don't support AP mode. So your network backbone will be two Windows computers linked with an ad-hoc connection. Stability is something you can forget about for sure

Wireless is not secure. You said that wired connection is not an option, so you will just have to take the risk. On a busy WiFi network, cracking the crypto keys is a matter of hours when using the computing power available today.

You could set up a VPN tunnel across the wireless link of course - that would be secure, it would also be a lot more work.