If you are going to be there a couple of months, something else you might consider doing is to take a trip to Thermopolis and enjoy the world's biggest hot springs, as least that's what the signs say. They also have some dinosaur digs and a buffalo herd, I think. Nice little town and about 1 to 1 1/4 hour trip from Cody. Also has the Windriver Canyon which has a lot of geological information spread along the canyon walls.
From Cody you can get into Yellowstone two ways, over Sylvan Pass or over the Chief Joseph Byway. The second way takes you down to a junction so you can go over the Beartooth Highway, a beautiful ride. Then you can drop down into Yellowstone and go by the Lamar Valley seeing Buffalo, perhaps wolves and probably bears, as well as Elk, etc. It will be a long trip that way, so get up early and pack a lunch. It will be worth it, especially when you top the pass going down into Yellowstone and see how massive the country is around that part of the world.
John A. Lichty