Sorry - off on a tangent - back to Paul - I don't really see a feasible way to increase the resolution of a screenshot in fedora (or otherwise). I think you'll always be limited by the screen resolution. I guess you could buy a HUGE monitor...... ;)
If you could give some more info about exactly what you're trying to render and how large (and maybe to what purpose?) I might be able to help - I juggle graphics all day for a living...
Chris