Running Mac OS X 10.2.3 on an iMac DV, connected to the home LAN by
means of an Apple Airport card talking to the Wi-Fi LinkSys BEFW11S4
router, with good to excellent link reception quality. When waking up
from standby, the Airport network name is systematically unselected in
the Airport menu (small icon at right of Finder menu bar) and needs to
be manually selected (effectively reconnecting the Mac to the network)
before launching Internet Explorer; otherwise error messages result. I
have monitored other Macs with similar setups not showing this
syndrome. I have searched all kinds of Internet resources for a
solution, to no avail. Can anyone help me solve the issue? I can
provide/find out more configuration details if need be. Thanks!

Go to System Preferences. Select the Network Tab. Then select the
Airport tab. Click the "Join selected network" and enter the network
ID and password (if you're using WEP). Click the Apply tab, and you
should automatically connect to the wireless network once you come
back from sleep.