this is an issue with your site because of its theme, not with c5.

mmm, I don't have IE natively to test with, but by looking at your site in Adobe Browser Labs, I see a few things:

1) You're using HTML5, but I didn't see CSS3Pie or Modernizr in your code to make HTML5 tags, like <section> work in IE 8- . I recommend using one of these solutions to enable IE 8 and under to be able to understand your HTML5 tags.
Modernizer:http://www.modernizr.com/
css3Pie:http://css3pie.com/

2) Also, you might want to consider a conditional comment for IE 7 & 6:


3) If your problems still persist after this, you'll have to add some conditional styles to your css. This is usually very easy, just identify the area that's acting screwy in IE, and start adjusting whatever you think is not working properly in IE w/ the following IE target codes in your CSS:
IE 8 & Under:
IE 7:
IE 6:


That should help get you on your way. Hope it helps!