You would set your flash on remote mode and then go in to your camera settings and set your on camera flash from TTL mode to Commander mode. Then pop the pop up flash up and take a picture, the pop up should fire a little flash and trigger the Sb-600. I have no experience with the D200 but I'm assuming it works this way as my D90 does.
If not then you can get a set of Cactus Triggers, Cybersyncs, or pocket wizards. Each one will enable your camera to wirelessly fire flash.