Here's the South Couty Trailway that will get you from the City line to Dobbs:
http://www.westchestergov.com/Parks/...ys/SCTrail.pdf
Air knows how to get up the west side; I'm sure you do as well, but PM him.
Here's the Master NYC DOT Bike Maps:
http://www.nyc.gov/html/dot/download...pfront2007.pdf
http://www.nyc.gov/html/dot/download...apback2007.pdf
Here's the Greenway guide:
http://www.nycgovparks.org/sub_thing...t-greenway.pdf