About how many pixels make up a website page? Like if you dont have any scrollbars, how wide and tall would it be in pixels?

depends on the users screen resolution.

that's when you hear about 800x600 or 640x480 or 1280xWhatever and so forth...

its the number of points of light possibly seen within the screen area.

I'd say use the 800x600 dimensions. I don't think many people have the small one anymore, and while the largest one is great, not everyone has that and the page won't be fully visible to the medium screen people.