Due to the lockout, the NBA will play a condensed, albeit two game, preseason. The Celtics open up the preseason in Toronto on December 18th and then close out the preseason at home against the Raptors again on December 21st.
The teams have to get a few games under their belts before they open up the season. The games will be ugly, but they are a necessary evil in this bizarro season. Regardless, the 18th still seems far away and even further away when your consider that there has yet to be a free agent signing.