It takes 40 Dems to filibuster.
I doubt Byrd, Nelson (NE), Nelson (FL), and a few red state Dems will filibuster. If they do they can kiss their Senate seats good bye come November 2006.
Somebody correct me if I'm wrong, but they need 60 votes to stop debate under current rules. That means they need 41 to continue the filibuster. Five dem defectors, without any pubbies being contrary, is the goal without a rule change, i.e. the Constitutional option.