if you are coming by international flight, you need a minimum of 1 hr to collect your bags and go through customs.. you should cater for 1 1/2 hr.
you will be in time if you take a taxi - $75 minimum + $15 tip to Newark airport - 1 1/2 hr, upto two hrs in heavy traffic.
You can ask one of the airport staff for suggestions or ask them to send you to the information desk.. who may help you.. but that will waste another hour.
DO NOT TAKE THE AIRTRAIN... that only takes you from JFK airport to Manhattan (centre of New York, in the opp direction)
http://www.youtube.com/watch?v=N-B72IIyoV4
jfk - newark