I have the oddest issue with my Apple iMac Intel Core2Duo. When I plug in an external monitor (even if it is turned off), my Airport wireless card can no longer get an IP from any wireless network, though it still shows full signal strength. Unplugging my external monitor fixes the problem. I have tried reinstalling OS X and replacing the Airport card to no avail. The issue also occurs in Windows XP under Boot Camp. Thankfully my computer has a 3-year warrantly and I will be calling the problem in to Apple. In the meantime, do you guys have any idea about how this problem could be fixed. It has baffled all computer experts I've talked to (myself included). The best answer I've gotten is it's a short-circuit issue with the motherboard.