starting a cluster

Ok as a proof of concept in my mind I would love to know how would be the
"easiest" method of being able to create a 2 cluster computer system using
debian to fully utilize two machines CPU cycles and ram alotments to run off
of a single pre-existing app?

Or is this *requiring* that I write my own app in principle I would love to
take some graphically intensive app and distribute it over both to allow for
a more speedy interface and or perhaps a more enjoyable interface.

All of the documentation looks like it was meant for a scientist but I'm
sure that there is a more down to earth proven version of this as I do have
experience with the unix/linux/debian/etc OS and variants for at least 5
years so I guess I can handle it.

Just asking what you would recommend for this and how would be the easiest
way to deal with it.

-- 
"The death of one man is a tragedy, the death of 10 million is a statistic"
-- Joseph Stalin

"Omnia mutantur, nihil interit"
(Translation:
Everything changes, nothing is lost.)
-- Ovid, _Metamorphoses_