Really, if you want quick and easy dynasty rankings, take your redraft rankings, take out the major rookies like Maroney, Bush, VD, Leinart, etc. Group the players by what you feel their tiers are, and then rearrange each tier by age of the player. Its not the most accurate, but it'll give you a good feel. Then with the rookies, you need to insert them individually, as they can jump up tiers because there's currently a starter ahead of them, but they're the future (see Maroney or Williams).
There should be some lists of compiled dynasty rankings here at the cafe too.