Oh, you mean 'Sup'. It's just a standard greeting. If you're ever in doubt about how to respond, an acceptable resonse is "Not much. You?"
As with most greetings, it has become fairly ritualized, but I find standard responses boring and usually try to reply with a description of what I'm currently doing/was doing recently. i.e. "I just baked some chocolate chip cookies, and now I'm trying to decide whether I should play Guild Wars or work on homework."

Edit: And, I dislike the word 'wigger'. It just sounds ugly.