It lists computers and services on the local network (Avahi) and hardware connected to your computer (HAL). When you click a device, it tells you properties of the device and lets you perform common actions for that device. For example, an ftp share has a button to open in Nautilus, a webcam has a button to open in Cheese and an inline preview of the webcam.
Install HardwareMap in Ubuntu Lucid and karmic
Open the terminal and run the commands
sudo add-apt-repository ppa:ccouzens/ppa
sudo apt-get update
sudo apt-get install hardwaremap