You will probably need to have a repeater, as well as some access points.

Or you could try::: Hawking Hi-Gain HSB2 WiFi Signal Booster - wireless network amplifier Networking Accessory reviews - CNET Reviews

This goes on your router. The antenna attaches to this device, and a wire attaches to where your antenna once was. On the device, you can choose between 100, 200, and 500 mW, which is the signal strength (higher is better). I've heard it does a fantastic job.

But in all likeliness, you will need to buy some repeaters with high gain antennas on them to be able to cover the area your wanting. You will also probably need outdoor omni's. If you keep the antenna inside, you will loose a lot of signal due to obstructions (walls, objects, etc...).

Borgslayer