I would definitely see about Beanie's injuries. If they're anything serious or looks like he'll be seeing limited touches then maybe.
But as of now, I think Beanie's too valuable to trade to get Murray. Reason being.. I know Murray had that great game today, but there's no saying that he'll be that great against a better rushing defense. and once Jones comes in, he's Number 1 in the RB spot so he'll probably get most of the touches. Cowboys really like to pass it a lot so Murray's chances aren't really looking good.
I like the Sidney for Harvin part but if you have to trade away Beanie and only get Murray for it, I wouldn't do it. IMO.