Now the web-trendies and accessibility gurus abhor table-based layouts it pays to gain some expertise with the Cascading Style Sheets properties position, float and clear in order to set your website out nicely.
There's a good tutorial / demonstration of the effects of position: static, position: relative, position:absolute, float and clear at BarelyFitz Designs - Learn CSS Positioning in Ten Steps.

Comments
Css tuts
Never really been into css.But i would like to suggest the following site as far as css floats is concerned.
Learn CSS Floats