Theme that does not stretch to any resolution

Hello, I'm using the Bluesquare theme.
Is there a way to set it not to stretch to any resolution, but to stay fixed on 1024x768?

I drew some nice smooth borders but on users with larger resolutions they loop and can't fit.
So what I need is, a theme that stays centered and fixed on 1024x768 no matter what the resolution of the screen is.

Any help would be great,
thank you!