To convert from milliseconds from epoch (assume epoch is Jan 1st 1970):
select to_date('19700101', 'YYYYMMDD') + ( 1 / 24 / 60 / 60 / 1000) * 1322629200000
from dual;
11/30/2011 5:00:00 AM
To convert that date back to milliseconds:
select (to_date('11/30/2011 05:00:00', 'MM/DD/YYYY HH24:MI:SS') - to_date('19700101', 'YYYYMMDD')) * 24 * 60 * 60 * 1000
from dual;
1322629200000
If its seconds instead of milliseconds, just omit the 1000 part of the equation:
select to_date('19700101', 'YYYYMMDD') + ( 1 / 24 / 60 / 60 ) * 1322629200
from dual;
select (to_date('11/30/2011 05:00:00', 'MM/DD/YYYY HH24:MI:SS') - to_date('19700101', 'YYYYMMDD')) * 24 * 60 * 60
from dual;
Hope that helps.