Smith for Marshall you could justify, especially given their respective ages. I don't really know that I'd make the trade, but you could craft a decent argument for it.
Matt Moore and Steve Smith to Denver for Orton and Brandon Marshall.
Moore for Orton, though? That part of it I have a hard time buying into. Orton is, and likely always will be, a pure game manager (probably better suited in his skill set to a WCO). If Moore continues to improve like he did through the last five weeks of the 09 season, we could really have something.
Yes, he could also tank, but it's all a gamble on some level anyway.