Hey yahoo unfortunately doesn't do nhl playoffs. Although I wish they would. An alternative is http://www.draftstreet.com/register.aspx?r=benbuck14 It's pretty fun and you get to make a team for every two days (or one game in each series) This way if one of the teams you went deep on gets bounced in the first round you can keep playing with a good chance of winning. Check it out and good luck!
It's free (Or you can bet on it if you want)
P.S. if you do check it out use benbuck14 as the referrer please