The serial output on the WL-500gP v1 is TTL so you first need to find yourself a converter for TTL to serial.
you can also get a direct usb <-> ttl cable like this: http://nl.farnell.com/ftdi/ttl-232r-...ter/dp/1329311

You should look around in some local electronic stores, they should be easy to find.
You can also build one yourself with an MAX232 chip for example