Current make-up of the Senate is 56 D, 2 Ind (Lieberman and Sanders), 41 R plus one disputed (MN).
Both Lieberman and Sanders caucus with the Democrats and will slavishly vote with them -- giving the D's 58 votes (including Teddy K).
But, to gain cloture, the Dems need 60 votes. Meaning, as you posed, they need at least two R's...plus Kennedy.
Judd Gregg has said he won’t be voting while his aappointment is pending. Of course on cloture no vote is as good as a ‘no’ vote, so that is ok.