A Guest Worker System would require a change in the law which I can support but those already in the US have already broken the law and should be rounded up and punished. They are criminals after all. Those who come in after a Guest Worker Program is on the books and is a law would not be criminals, obviously, and should be given the same basic employment rights that everyone recieves, such as minimum wage limits, workman's compensation, tax responsibilities, and so forth.
I am totally against any sort of amnesty for those who are already criminally inside the US.