Have you thought of a High Gain Antenna replacement.
http://www.linksys.com/products/group.asp?grid=33&scid=38
****************************************************************
802.11b vs 802.11g
First the 802.11 is an unregulated frequency and can accept interference from appliances such as microwave ovens, cordless phones, and other appliances using the same 2.4 GHz range. However, by installing 802.11 gear at a reasonable distance from other appliances, interference can easily be avoided. But be aware that moving your router to a different location can result in better/worse performance.
802.11b
802.11b supports bandwidth up to 11 Mbps, comparable to traditional Ethernet.
802.11b uses the same radio signaling frequency - 2.4 GHz - as the original 802.11 standard.
Pros of 802.11b - lowest cost; signal range is best and is not easily obstructed
Cons of 802.11b - slowest maximum speed; supports fewer simultaneous users; appliances may interfere on the unregulated frequency band
802.11g
802.11g supports bandwidth up to 54 Mbps, and it uses the 2.4 Ghz frequency for greater range. 802.11g is backwards compatible with 802.11b, meaning that 802.11g access points will work with 802.11b wireless network adapters and vice versa.
Pros of 802.11g - fastest maximum speed; supports more simulatenous users; signal range is best and is not easily obstructed
Cons of 802.11g - costs more than 802.11b; appliances may interfere on the unregulated signal frequency