I'm having the same exact problem. I'm connected by DHCP with my wireless from my iBook. I always connected find on LimeWire. Since yesterday, as soon as I launch LimeWire, I loose my wireless connection. The only way to get it back is to restart the computer because doing a "renew" from the dhcp doesn't work.

The only thing of importance that I can recall doing from when it worked and yesterday, is updating my Airport software to the latest version... I'll try to uninstall that update and see if makes a difference.