Don't know if this is a fed law or just state-dependant, but in Colorado we don't have to smog until a vehicle is four years old, and then it's every two years after that.
I do know that if you fail your smog test, they give you a list of approved auto mechanics. If the approved shop signs a ticket saying that the problem cannot be corrected for under a certain limit (something like $500), then the smog facility will waive your vehicle. This is really intended to assist people with older cars I believe.
-Pace