The cookies can be baked weeks ahead and frozen. They can be iced several days ahead but better if done just one day ahead.
Some have gone so far as to ice them completely - making totally *SURE!* they are dry before freezing them. If you do that you have to use wax paper between layers (not more than 3 layers) and be sure you set them out single layer to thaw. Make sure they are in a covered box that is wrapped in plastic for thawing.
I prefer to ice my cookies two days ahead, just in case. Gives a little more time to dry and allows for fixing/replacing "oops" cookies. Definitely love the ability to freeze the baked cookies and thaw (kakeladi's advice is spot-on) before icing.
My Grandma always used to make iced cookies dozens at a time, and put them in tupperware, separated by a layer of plastic wrap. If you make your own icing on the stove instead of using the store-bought stuff, the icing will melt in your mouth if you eat them cold. That's what Christmas tastes like at our house.
Definitely freeze them, use wax paper or plastic to separate them, but don't put them into the cold until the icing is completely cool.
I work for a cookie company, you may have heard of them... http://www.mrsfields.com/ If you don't have time to bake it yourself, Mrs. Fields can!