Does anyone have any tips for designing on a 1200x800 screen, because I know most people use 1024x768 but I don't want to have to change my resolution. I want to get everything aligned in most resolutions without having to change mine.

If you want to take a look at some of my coding, feel free. I use a 1200 x 800 res and my stuff looks fine on smaller ones.

Have you ever considered making a layout that stretches horizontally? This is one case where it's actually okay to use percentages, lol!

You would just set the width to 100% or 90% and then for the header, pick a pattern (like maybe a gradient or something) and have it only repeat horizontally. Use only a solid color/borders for your content background so you don't have to worry about a repeating background that isn't wide enough.

I mentioned using 90% because that way you can have a layout with some background space on either side. You can put a tiling background image here.

edit; For non-fluid layouts, how are you positioning them? Can you show me an example? That way I can tell you exactly, for that type of layout, how to make sure it doesn't "float" when you change your resolution.

i also use 1200x800, but when i make layouts i stick to pretty much the same sizes i was using before, when i had 1024x768.
if anything been finding ways to make my layouts centered

also i use a script that resizes my browser to most screen resolutions
http://www.rjlsoftware.com/software/utility/resize/

its free and works just great for me