If, like me, you have a MacBook Pro -- or any other machine which has problems staying connected to a wireless network -- here's a quick and dirty fix. What I've found is that pinging the router continually prevents the loss of connection. I then minimize the Terminal window with the ping task, and all is well.
[robg adds: While solving the problem would be a better solution, this is a functional workaround. You could reduce the system impact a bit by using something like ping -c 2 192.168.1.1, where 192.168.1.1 is the router address. The -c 2 bit tells ping to stop after two responses. Then use cron (or Cronnix, a GUI front-end for cron) to run that command every few minutes -- just often enough to keep the connection alive.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061126132814130