Yeah, I've had great success with the Method 2 from sun7dots example site.
I adapted eric meyer's "Pure CSS popups with images" though from http://www.meyerweb.com/eric/css/edge

The css and html validators from w3c should become your friend. They won't guarantee success, but they will atleast point out any serious flaws.

The inclusion of a doctype is important, because it often changes the way a browser parses and renders the underlying html/css. Often without one the browser goes lazy, and causes weird results. Ofcourse every browser is unfortunatly different.