Wireless Networking on a Farm

Hello,
I've done some research on how to go about this, but have not been able to find anything definitive. Basically, I have an airport express hooked up in my house and I want to extend it down to my garage and my barn. The house is clad in aluminum siding and both the barn and garage have steel siding. The far end of the barn is about 350 feet from where the express is set up. I am running a 17" powerbook g4 with an airport extreme card.
I realize that airport express units can be placed in various locations to extend the network, but I don't think I want to have any sitting outside. So basically my question is: what is the easiest and cheapest way to go about this?
I'd really appreciate any suggestions or advice.
Thanks.

put it on the closest wall to the place where you want the signal to go. Also if your house is a multi-level house, put it on the highest level. Most likely if the space between your house and barn is just a field it will likely get there pretty easily. You'd be surprised how far they travel with such little power.

In a heavily metal clad and long distance environment like that soho equipment is going to be a bit hit and miss unless you can try it out first ...borrowing a couple of airport expresses maybe?

The ideal solution is cabling as much as possible. As it's the most robust and reliable solution. Cable to a convenient point and then connect an airport express as close to where you'll use your notebook.

Are they all on the same electricity ring main by chance? If so you could you ethernet over power adapters (1 in the house, 1 in the garage and/or barn). Then connect an airport express to the garage/barn adapter.

Ethernet cable under ground?

Thanks, I don't think they are on the same ring, though I'm not positive what that means. Basically, each structure has its own electrical box which gets its power from a central pole.
What do you mean by "ethernet over power adapters"?
The garage is a somewhat central location--150 feet from the barn and from the house.
There is also a phone jack in the barn and we get our internet via DSL. How easy is it to set up another DSL location?

To set up the dsl over the phone line, I'd think you'd need another modem. I personally would go the ethernet cable route... put it inside some plastic or metal pipe and run it a few inches under the ground, then on the end set a wireless router up

If this is mission critical to you, then cable is the only way to go. Not sure where you are based but you can buy direct bury network cable in most countries. Actually a little research via Google revels a number of folk's who have used standard network cable in either plastic or metal piping to protect it when buried.