It sounds like you're having the same problem that I was having when I was using Panther. I went to the Mac Genius at the Apple Store near here and he helped me. You have to clear your preferences out and restart the computer and it should work fine after that. One thing you can do to make sure it is having the same problem is after it wakes back up and won't reconnect, go to System Preferences and go to Network. If it shows a yellow icon for Airport, that means it is connected but can't get an IP address. GO to your Mac HD > Library > Preferences > SystemConfiguration and clear out the preferences that have to do with Airport, Network, and the one that is just called Preferences. There are 3 that you need to delete and then restart... That fixed my problem and since I upgraded to Tiger, I haven't had anymore problems.