The stretch I did was from Potsdam to Brandenburg. I didn't really know it existed and just planned to do the stretch on road, but it was a revelation. Berlin to Potsdam is easy enough, and you can do the majority of that on traffic-free or quiet roads through Grunewald.
I would love to go all the way to/from Berlin, how much time are you allowing?
http://www.reiseland-brandenburg.de/themen/radfahren/havel-radweg.html
http://www.havelradweg.de
The stretch I did was from Potsdam to Brandenburg. I didn't really know it existed and just planned to do the stretch on road, but it was a revelation. Berlin to Potsdam is easy enough, and you can do the majority of that on traffic-free or quiet roads through Grunewald.
I would love to go all the way to/from Berlin, how much time are you allowing?