Mac Geekery has some basic advice on optimizing airport wireless reception. I don’t really think it’s Mac specific either. Basically, you want to survey the wireless access points in your vicinity and make sure you are using a unique channel.
It seems to have worked here. I was on channel 9, which is the default for the Qwest Actiontec, and there is another Actiontec around which is sharing the channel. When I moved to channel 3 (via advanced configuration in the Actiontec web configurator), I got much better download times – 800-1000Kbps compared to 300-500Kbps. And it looks like it’s sustaining that.