I have a Netgear Rangemax wireless router that I want to make an invisible network with. At the store the woman called it "stealth" but I've found neither of these things on the Netgear website nor in the settings for the router.

How do I do this? Do I need a different device? Replace the firmware?

Start with turning off the SSID, but remember what it is so you can connect yourself. That stops the broadcast of the wireless ID. It's not 100%, but does hide the wireless from 99% of the people out there. hackers will still find it...you need good wireless security regardless....