How can I take busses or trains from any station in Boston, MA to the Poughkeepsie, NY station?

You can also take BoltBus/Peter Pan/Megabus to NYC, then MetroNorth from Grand Central to Poughkeepsie. Or Amtrak to NY Penn Station, then get to Grand Central for the Poughkeepsie train. There are more Metro North trains than there are Amtrak trains, and they are cheaper.