Sidebar problem

I am using the theme for a blog for my wife, she really likes it a lot.
There is however one problem i can't solve. Everything works fine in Firefox but in Chrome and IE rhe sidebar dissapears to the bottom (under the footer) when reading the comments.
I've tried changing the width, padding etc. of the sidebar and the main content area in the style.css, but nothing seems to work.
Could you point me in the right direction.

Here http://http://www.dineke.molema-smit.nl you can see what i mean or see the attached file.