Smithsonian Magazine Museum Day Live! is Saturday, September 29, 2012. It's very easy to get your free ticket for two to a participating museum. All the details here:

This offer is only valid on Saturday, September 29th (exceptions for Museum Day museums closed on Saturdays). It's a free ticket for two at a participating museum (participating museums in Montana are Missoula Art Museum, MonDak Heritage Center, Montana Historical Society, Museum at Central School, Museum of the Rockies, Ravalli County Museum, The Children's Museum of Bozeman, Western Heritage Center and Yellowstone Art Museum).

Just fill out some brief information HERE and get your free tickets emailed to you (you must print it to receive your free admission).