The Tokamak physics engine does dynamic collisions, though the physics stuff may be more than you're looking for. Sweenie's working on a wrapper to allow Tokamak to be used in Blitz at the moment. Check out this thread for more info.
http://www.blitzbasic.com/Community/posts.php?topic=29381
http://www.blitzbasic.com/Community/posts.php?topic=29381