Changing screen size along with screen resolution?

[Lance Simmons <lance@lsimmons.net>]

I know how to change screen resolution using ctl-alt-plus or
ctl-alt-minus, but the absolute size of the screen doesn't change. Is
there a way to change resolution _and_ screen size at the same time?

I usually use 1600x1200, but now I'd like to run a linux game
fullscreen at 800x600. That leaves me with a screen four times larger
than I want.

Any suggestions?

-- 
Lance Simmons