"Matter can be thought of as compressed energy in a sense, but that trivializes the difference between the two. Light, heat, gamma rays, etc, are energy, while my desk is matter. "
But you see there really isn't any difference between the two (atleast that's what my two physics student flat mates told me, so if i'm wrong RobS is welcome to jump in and tell me so) mass is considered to just be another form of energy, no less so, than light, heat, etc.
"I suppose if people were to somehow become translated into energy a material source would be necessary to effect this change, but once converted, wouldn't need the material source"
It is simply not feasable to "convert" people into energy, photons are vastly more simply in terms of number of possible interactions than matter. They also can never stand still!
". Light from the sun doesn't need the sun once it's produced. If the sun were to vanish immediately, we'd still have eight minutes of light coming our way. "
But light from the sun is just a stream of photons, you cannot reproduce complex systems using just photons.
The only way you could consider doing this, is by somehow scanning a human being, there disintergrating him, then building him from the ground up. At the point during the two phases our human being would just be a bunch of 0s and 1s on the computer, thats about as close as you can get to "pure energy". Furthermore even that scenario is horribly flawed; You would need advancements in nanotechnology that are simply unrealistic (we are talking about individually placing every molecule in every cell, in a specific position, even if you somehow generate all your cells biologically then try and fit them together its stil pushing the bounds of realism by quite a long way), AND you would need a hard drive the size of a galaxy to store the information..... i don't think so, its just not a feasale scenario at all.
I have read the articles on the number of computations the universe could do before. But, its simply a theoretical calculation that albeit interesting most physicists believe doesn't actually have a physical meaning. (There was an article in the New Scientist about it a couple of weeks ago).