Hi There,
The first thing you can do to improve distance is upgrade your antenna. This can be done either at the router or at the remote computer. A Good 12+ db Biquad can be had for around $20, Or you can build one yourself. The Biquad can be used "stand alone" for about 12-13db gain, or combined with a small satellite dish for about 28-30db gain. They are very directional, giving good long range connections, and good "backside" rejection of unwanted signals. They are very small (about 5" square) and by far the best design that I've researched, so far.
For High Quality, Weatherproof BiQuads Check Here:
http://www.thewifipro.net
or here:
eBay Seller: thewifipro: Computers Networking items on eBay.com