Wireless Internet: Looking for ONE powerful wireless base station for BIG house

Looking for ONE powerful wireless base station for BIG house

Hello

My parents have a large house in California. About 7000 sq ft. We are looking for a wireless solution that will suit their needs. They have standard DSL service. They have an iMac, a Powerbook, and a Mac Book Air. Also 2 iPhone 3Gs.

They also have a second home in Idaho which has its own Airport base station and which seems to work fine (because there is only one).

I currently have them using an Airport base station and 2 airport expresses in the California house. The relays constantly drop, and it's hard to get them to log into the correct base station in the correct part of the house. They are constantly confused about the whole thing.

I think the solution is to get a VERY powerful base station (any manufacturer will do) which will allow us ot set up ONE wireless network and name it "California". Then they can come home, log in, and not worry anymore.

Any ideas here? Can anyone suggest a single wireless router or station that will support a 7000 s1 ft home through walls and 3 stories?

Thanks