I am trying to figure the difference in hours between two date time
fields which involves different time zones. The one element that will
never change is the one time zone will always be eastern time
(philadelphia, pa, usa area). the others time zones will always be
ahead, for example to get the correct time in Austrailia, I would need
to add 14 hours to the time here. Can you help?
example of dates; 07/13/12 @ 8am a shipment leaves Melbourne,
Austrailia, it arrives in Phila, pa, USA, 07/15/12 @ 6am. How can I
caluclate the elasped time between the two dates?

If A1 has the Philadelphia date/time to receive, B1 has the local time in the other time zone to send, and C1 has the number of hours ahead, then maybe this would work:
=A1-(B1+TIME(C1,0,0))
Format as desired, maybe
d h:mm
or
d "days" h:mm