columns within tabs

Hi there ...
First, apologies, I'm always real slow on the uptake when it comes to CSS
stuff.
I was trying to set up a tab with a basic two column layout using
float. I find that as soon as I float a div that it pops out of the tab
box (you can see this using the example.html file, wrap the lorem ipsum in
tab 1 with a div and give it a "float: left" style). Is there some way of
getting this to work?
Thanks
-J