With the switchover to phpBB3, some features that we had on ProBoards are missing, which includes dice rolls. Until that feature can be added, there are some temporary solutions for dice rolls that can be used in the meantime. Our new AJAX Chat/ShoutBox feature does have a '/roll' command, which generates a random number 1-6. The results are displayed on both ShoutBox and in 'Live Discussion'.
Another alternative solution is this website:
http://invisiblecastle.com/roller/
I heard about this from some of the posters on phpBB3 while looking for some info on phpBB3 dice roll development. Some said that this site could work as an alternative until a real dice roll command is developed for phpBB3.