Twinkle, when you get off the plane, head for the Ground Transportation Centre in Newark airport(well signposted in my memory!) and ask about buses and shared taxis.
We got a shared taxi and it's basically a minibus that drops you off at whichever hotel you're staying at. i think for us it was about $12 each (2006 prices though!), but you can price which one is best for you.
For the return journey, most (if not all) hotels run a minibus service from their front door back to the two airports, but you usually have to book onto them a day or two before leaving.