I'm trying to create a three column layout in CSS only with fixed left and right columns and a fluid central column. I have searched online but nothing has worked when I implement it. I don't know whether this is particularly relevant but my central column is (or contains, I've tried both) an iframe. This seems to be contributing to the complication.
Have you tried using an 960 grid ?
Otherwise there are many examples for using fixed and fluid grid layouts in the web:
http://www.dynamicdrive.com/style/layouts/item/css-liquid-layout-31-fixed-fluid-fixed/ This is the one you are looking for.
Btw: Please provide some of your code, or do a jsfiddle about it !