Using your airport card as a wifi router and hiding the SSID?

I am using my iMac's airport card as a wifi router but I don't want to publish the SSID name to the whole neighborhood. I did password protect the network using WEP encryption but I do not know how to make it a hidden network. I have used before external wifi routers that allowed me to do this, but I can't figure out how to do it on the iMac (SnowLeopard). Can it be done?