Problem is that graphics and text at 800x600 resolution look crap when I change to 1024x768.

Okay, first thing... you're not developing on an LCD monitor, are you?

Second...

What everyone is trying to say is:

Don't develop to a specific screen size. Your web page should be designed so that all of the screen objects (tables, paragraphs, frames, images, text wrapping, etc.) re-flows logically around the page and looks good with the browser window at ANY reasonable size and shape, from as small as 640 to as large as 1600. When this is done correctly, your page does not need to detect the screen size or do anything special. Test this by viewing the page on a high-rez screen and resizing the window and looking at how it flows. If something doesn't look right, fix it by using things like tables, the <nobr> tag, and spacer-gifs.

A web page that only works at one screen rez is a sign of a newbie web designer.