This panel, radically redesigned for Leopard, shows up only if your Mac is equipped with a Bluetooth transmitter, either built-in or in the form of an external USB gadget.
Bluetooth is a short-range, low-power, wireless cable-elimination technology. It's designed to connect gadgets in pairings that make sense, like cellphone+earpiece, wireless keyboard+Mac, Palm organizer+Mac, or Mac+cellphone (to connect to the Internet or to transmit files).
Now, you wouldn't want the guy in the next cubicle to be able to operate your Mac using his Bluetooth keyboard. So the first step in any Bluetooth relationship is pairing, where you formally introduce the two gadgets that will be communicating. Here's how that goes:
Open System Preferences→Bluetooth
Make sure Bluetooth Power is turned on. (The only reason to turn it off is to save laptop battery power.) Also make sure Discoverable is turned on; that makes the Mac "visible" to other Bluetooth gadgets in range.
Click the + button below the list at left.
The Bluetooth Setup Assistant opens, offering a list of typical Bluetooth equipment that your Mac can talk to: Mobile Phone, Headset, Printer, etc.
Click the kind of gear you have, and then click Continue.
The Mac whirs for a moment, and then displays the names of all Bluetooth gadgets that it can sniff out. Usually, it finds the one you're trying to pair.
Click the name of the phone/headset/keyboard/whatever, and then click Continue.
If you're pairing a mobile phone or something else that ...