Mac Specs: MacBook 2.4 GHz, 4 Gb, 320 GB 7200 RPM WD Scorpio, OS X 10.6.2, Win 7
Click on your Airport icon which sits in the top menu. A drop down list will appear with the SSIDs of the networks which are in range along with some other options.
Additionally, you can use a WiFi sniffer to view hidden access points and statistics. The only one I know of that works with 10.6 (Snow Leopard) is AirRadar.