Make sure you have the device connected to your PC. Using the provided null modem serial cable, plug it into S1 (AUX) on the device and into an available serial port on your computer.
Click Start --> Programs --> Accessories --> Communications --> HyperTerminal
When the program first runs, it'll either prompt you for an area code or name. If it prompts you for an area code, provide one and click OK. It should then prompt you for a name. Any name will do.
On the next screen, for "Connect Using", select the serial ("COM") port that the device is connected to. Click OK.
On the next screen, change the Bits per second to 38400. Click OK.
The next screen should be a blank window. Hit enter a couple of times and you should see a login prompt. The username is "admin" and the default password is also "admin" (unless it was changed).
Note: Vista users will need to install HyperTerminal or download a free serial program such as PuTTY.