Full Screen games and Large widescreen monitors

[2dav01]

I run a large Tv as a monitor through an HDMI output, but almost all of my games will not run in full screen. I have read about windowing games, but it seems as though no 3rd party software exists. Aside from windowing a game is it possible to reduce the entire display size on the screen so that there is a blank border around a fixed windows resolution?

I run:
Windows XP
Onboard Video (Radeon)
Athlon 6000+
37'' LCD HDTV