Like others said, folow the signs for the Airtrain to the NJ Transit stop at the airport, buy a ticket at the computer, take NJ Transit to the last stop (Penn), cab it or subway depending on your preference.
although i haven't taken it, i don't believe there is a train directly from newark airport to penn station. you have to take the monorail from the airport to the newark amtrak/nj transit terminal, then train it to manhattan. you might also be able to catch the PATH train there, which would take you to mid-town, IIRC, there's a stop around 34th and 6th (aka ave. of the americas). F/V/B/D trains to 47-50th and you're there. You're staying at the Hilton? 53rd and 6th?
$60, w/ tax, toll, and tip, to mid-town from newark. i don't understand why sam couldn't just send the limo for you tho...