youll be surprised how easy it is, i'm gussing the rutgers stop is new brunswick on the princeton line rail? if so, youll either go to newark pen and transfer to another train going to ny pen, but most likely theres one on that line (never been on tht line myself) that will go direct to ny pen.
Go here for the rail map:
http://www.njtransit.com/sf/sf_servl...SchedulesMapTo
Go here to get scheduals for the trains so you know when to get on it at rutgers and when youll get to pen.
http://www.njtransit.com/sf/sf_servl...ainSchedulesTo
From there, use the subway map to figure out which subway to take. best thing about the city is that even if you get on the wrong subway itll atleast get you close haha and then just hail a cab!
Go here for the subway map:
http://www.mta.info/nyct/maps/submap.htm