As I have stated in the Blog elsewhere, the Celtics will be participating in the Orlando Summer League. Unfortunately, the Orlando games are not open to the public. I believe they may be shown on NBAtv. You should be able to find out by Googling NBA Summer League/Orlando or by going to the NBA site.
I saw them at the Las Vegas Summer League the year we drafted BBD...Pruitt was there too, and it was terrific. I live in Florida and wish we could run over to Orlando to see them, I would be the first in line!
Last year it was a little before, but overlapping the Vegas games by a couple days. (A few of the unsigned players went directly from Orlando to Las Vegas, playing in both.