Help With CSS Fluid Layouts

Could anyone assist me in making this layout fluid:

I have never done a layout using div’s before, Nokrev said to use faux columns and all that but I didn’t understand and he neglected to explain properly. If anyone could help me out that would be cool.

Basically all that needs to be done is make the 3 columns in that layout expand vertically (fluidity) and I know how to do it with tables, but not with CSS.