For a start you should be using div id instead of div class to reference your div's in the markup. I dont think thats whats causing the problems tho.
As you've specified float:left on the leftContainer you don't need to specify float right on the rightContainer.
Also specifying widths on two elements floated next to eachother seems to cause problems sometimes. I'd keep the width on the leftContent and specify width:auto in the right content.
If it still doesn't work put in left-margin:221px in the rightContent to push it into place.
As for the footer, is there any real need to specify 900px with in the footer container? I try to stay clear of specifying widths unless I really have to because it can cause problems in ie.
Let me know if this has helped.
