It depends what camera you are using. If you camera has a "commander mode" than the sb-600 will work very well as a slave. If you are using a D60 or the more consumer cam's than you most likely don't have a TTL Commander mode.
So tell me your camera because with a D60 and a SB-600 you are pretty limited as far as the use of the flash.
One option that will work either way is the nikon sc-29 which can be found
Here.
It is a cord that attaches to the hot shoe on your camera and than onto the hotshoe adapter on your flash. Pretty straight forward as to what it might do right? Now, that chord has a bungy type of texture and you're only really comfortably using this for about 2 feet. Note that unless you are great at one handed shooting this can be hard. Get an assistant.
So yeah, do some reading cause I cant do that part for you.
1. Does you camera have TTL Commander mode? If Yes, you're done, set your flash to slave and shoot (This requires you reading your camera manual and flash manual, which you're already done, right?
2. Go buy the sc-29, you'll be restricted greatly and it might not be what you had in mind but you are currently restricted by your gear.
Hope that helps.
EDIT: I realize the flash cord is advertised for the Sb-800 but I just tested it out on a D90 + SB600 and it worked perfectly.