Subject: Is there a definite amount of moving mass for photons?

I posted a question earlier asking why photons are affected by 
gravity.  The answer I recieved was that photons do in fact have 
mass but only when moving.  That answer in turn has sparked a 
slew of questions.  But most importantly what are the properties 
of moving mass?  Does it have kinetic energy?  How are photons 
created?  Those are the main questions I have. But if elaborate 
more on any other "interesting" facts about particles without 
mass.  I would be more than happy to recieve them.

Re: Is there a definite amount of moving mass for photons?