Update.
After investing lots of time, hair pulling, resetting the wireless router to factory settings, messing around with the Mac Network Preferences, running periodic tasks, rebooting...nothing.
Then I found
http://forums.cocoaforge.com/viewtopic.php?f=13&t=17667&sid=27524bc75167be117ad3d5fedd3a5a87&start=20
Its an oldie but worked for me. IChat still doesn't work. But Adium does..for now. Fingers crossed.