Here is some random text to show that text flow extends the height of the box as needed. It sould reflow as you resize the window.
This reveals a weakness of the approach, the heights are not the same.
A little more filler text..
This is done here using nested divs for the columns.
The outer div for each column is floated left, has its width set to the relevant percentage and its margin, border-width and padding 0px. In order to illustrate what is going on, these have been given pale coloured backgrounds.
The inner div for each column has any required margin, border or padding. In the example, these have non-zero margin, border, and padding and a slightly darker background than the corresponding outer div.
There is another div surrounding the whole lot with a non-zero margin, border and padding. For this to work in later versions of Internet Explorer, the doctype must be set to make it use standards mode (it probably does not work in earlier versions of IE).