Here’s a post for beginner HTML/CSS soon to be ninjas. About 90% of the sites I have built use this same technique for layout. I generally use a 950px wide layout but this can be any size you would like as long as you adjust the width of the columns accordingly.
1: Set up the HTML
2: Add the CSS
Believe it or not thats all you have to do for the layout. Just remember if you are adding a border to the left_column or right_column that you are increasing the overall width of each column.
Check out a little demo page I created.