Wireless network- poor signal strenth

[Bethyk]

We have a Lg. home - over 10,000sqft built in a "U" shape. The center area is a courtyard with swimming pool etc. At the rear of the property is a guest house. All the DSL wiring for internet, phone, gates, and Coax for sat. etc comes into the house to a small room at one front corner. I am struggling to get a consistent, strong wireless signal inside the guest house - as well as the part of the main house farthest away from the control room.
I have tried adding a high gain (15dBi) outdoor antenna mounted to the top of the house, and a repeater with an indoor window mounted high gain antenna. The signal is STILL shaky at best and frequently drops altogether.
Can anyone suggest a better way to put this system together? The location of the router is not ideal, but there isn't a better place for it. Some of the signal issues I think, are due to the thickness & materials of the walls. Even a desktop with a good wireless card installed only picks up 2 bars consistently at approx 25ft from the router. I'm using a dual band wireless N router from DLink.
I am open to any suggestion - regardless of cost. Of course, I would prefer not to spend thousands, but function is vitally important.
Thanks for any help you can provide!
B

 

[MysticMiner]

Ok, then I'll suggest installing networking cable to where you want access. Except maybe the Guest house, that might not be allowed by code.

 

[Bethyk]

Perhaps I should have been more specific... I'm open to any WIRELESS solution... the house is all Venetian Plaster and stucco etc... It would take days to wire not to mention the sheer volume of cable... I'm looking for something relatively faster & easier... Sorry if I appeared to be missing the obvious. B