Farm Wireless Integration

I live on a large farm in rural Tennessee. I am on the north side of a ridge, about half way up the mountain between its peak and the creek and valley below. I have DSL because that is the only kind of high speed internet available to me out here. Right now I am building a loft apartment in the top of a 150 year old barn. It should be pretty cool. I am wiring it for water and power, but there will not be a land phone line in there. Obviously there wont be a server or any high speed internet wired in there. Just too remote. The main house where I have the DSL is 400 feet away from the barn, and the barn is also down about 30 feet in elevation. My question is, will i be able to get a wireless signal down to that barn from the DSL at my house? Right now i have a netgear wgt624v3 router, an apple airport express and an apple airport extreme. What other additional parts and accessories will i need to get a signal in my barn. Theoretically it would be even better to get a wireless signal over an area of about 100 acres. This would allow me to use the wireless system as a walkie talkie/ communications system throughout the farm. That might be pushing it. Dont know - I am no expert. It would be great if I could integrate the pieces I already have into a larger system. If i have to, I am willing to buy any and all pieces new. Thank you in advance.

addendum: i use mac products, or try to use mac products, exclusively on the farm. their simplicity is a lifesaver. dont know if this will make any difference. could get a dell if i have to set this up on a pc i guess (dont want to though )