Sorry for the delay. It's been a very busy day.
There's nothing wrong with the tabs or code. The problem is you have some oversized images which flow under the sidebar even in Firefox. IE is less tolerant of images. There are images of 700px in a space considerably smaller.
Keeping in mind that there's padding and margins around the content area of about 25px on either side, when you look at Dashboard > PageLines > Site Options and see the width of the content area. Subtract 50px from that and you have the maximum image size you should use. I do not recommend scaling the images as IE doesn't use or handle image scaling and the problem will persist.
Images should be resized in a graphics editor.