This ALA article by Rich Rutter rehashes an old 2002 method devised by Owen Briggs for sizing type consistently across browsers. It’s how I most often size type.
I do, however, prefer Briggs’ 69% or 76% on the body tag to Rutter’s 100%. Briggs’ way, 1em (rather than 0.875em) looks either like 11px or 13px, which are key sizes at which Verdana and Georgia were purposely designed to look nice. This does make the math a little more complicated when you try to achieve a baseline vertical rhythm, but that’s ok with me.
So, read up on that Rutter article. I also set up a new shell today, with some starting point typography styles.