I am running leopard, I can't remember what the latest update was off the top of my head, but that is installed. There are a lot of wireless routers around me and that seemed to be the overwhelming theme with my search when it came to this problem. From what I have found, if your connecting to a linksys router and there are other linksys routers around it could cause this problem. The funny thing is it only does it when it is disconnected from the power cable and is running on battery. It really does not make any sense, I really haven't had much time recently to fool around with it so I haven't been able to try some ideas I have and what the last post has in it.
If I find any sort of conclusion as to what could be causing it, i'll be sure to post it up. For now, I am still fighting it.