I recently moved to a new location. After re-installing my Airport Extreme and Airport Express, the network seems to work fine with one exception. When my G5 (3 years old) goes into sleep mode it seems to lose connection with the network. That is, when it comes out of sleep mode, the airport signal strength is in shadow so that I have to put the cursor over it and click on the drop-down name of my network name to reconnect to the network. How can I keep my computer from going off-line during sleep mode? It never used to do this at the old location, and I can't figure out what I've done differently.
I'm having the exact same problem with a 3 year old dual 2.5GHz G5. Computer wakes up and no signal, must re-select and all is good....but it's a pain! I called up Apple tech support and they told me to go into the Network panel of System Preferences and delete all the old networks "locations." Then when you try to join the network again you are forces to create a new "location" complete with entering in the base station password. I did this and things got quite a bit better. But I'm still finding the problem about half the time. Weird, huh? So I went just now to look at my settings and I had the "By default, join:" pull down menu set to "preferred networks." Maybe that was the problem. I just switched it to "Automatic" for both the "By default, join:" as well as the "Location:". We shall see! I was going to put up with this behavior for a couple weeks until I saw your post, thus prompting me to fiddle around with the settings again. Either that, or wait for an AirPort Extreme (n) updater to fix this bug with the G5's.