If you have a Windows Vista PC, and your wireless network does not broadcast its SSID, and you find yourself tearing your hair out because you are having trouble getting on to your wireless network even though you have checked a zillion times that you have the correct client settings, try this:
Go into your wireless router's settings and check "Broadcast SSID" (or uncheck "Do not broadcast SSID") before trying to connect again. Once you have established connection, you can go back into your wireless router's settings to disable the SSID broadcast setting. (which btw is not necessary if your reason for disabling SSID broadcast is security. Look here for a detailed discussion on this topic.)
So far, I had the same experience with three different Vista PCs and two different wireless networks and each time, enabling the SSID broadcast for the initial connection between the Vista PC and the network solved the problem.