Let's say you use your laptop to access the internet at Starbuck's, though why you'd pay to use their service I don't know. The SSID (name) of all of their access points are called T-Mobile after their provider. Your laptop remembers the SSID, and the next time you start it up, it tries to associate with it.
So here's the hack. I create an access point named T-Mobile. Your computer boots and says "Look! There's T-Mobile! I wonder if it will be my friend?" Your laptop is now associated with my access point and is now a little bit on the vulnerable side.
First solution: firewall. Don't use the Window's firewall, get something like Zone Alarm Pro. Second, NEVER associate to ad hoc networks. Always have your card to only associate with infrastructure networks. Apparently new laptops that have built-in wireless have a button to turn the card off. They recommend using said card when networking is not in use.
Anyway,
Here's The Fine Article on Slashdot that includes a link to the source story.
Important stuff if you're a Windows user who does wireless networking!