The museums were open in 2009 and they have been open in the past on inaguration days

http://www.gosmithsonian.com/inauguration/

This time around because its the same president it will not be as crazy as 2009. There will still be the parade and various inaguration balls happening.

Bush II second term was a little lower key than the first one. I expect the same with Obama where it isnt as crazy as 2009.

There will be security hot spots along the parade route which will be times for the president to step out of the car and walk on the street.

Inauguration Day falls on Sunday every 28 years. The last times this has happened when the person in office was an incumbent (Reagan, eisenhower) they did the oath privately on Sunday at noon but the parties/ceremony/parade have happened on Monday.

I dont know what will happen this time around...havent read anything.