Add a wireless repeater. Wireless repeaters extend your wireless network range without requiring you to add any wiring. Just place the wireless repeater halfway between your wireless access point and your computer, and you'll get an instant boost to your wireless signal strength. Check out the wireless repeaters from ViewSonic, D-Link, Linksys, Buffalo Technology and Belkin.
It would also be better if your wireless repeater is the same brand as your wireless router. Some vendors offer a performance boost of up to twice the performance when you choose their hardware. (i.e.) Linksys has the SpeedBooster technology, and D-Link has the 108G enhancement.
Move the router off the floor and away from walls and metal objects. Metal, walls, and floors will interfere with your router's wireless signals. The closer your router is to these obstructions, the more severe the interference, and the weaker your connection will be.
Hope that helps! Good luck with setting it up..hehehe