CSS question: IE7 alignment issue

Setting up a new site home page and trying to learn CSS. The page looks okay in
Firefox on PC and Safari and FF on Mac, but several alignment issues on PC.
First, header div isn't aligning left with container div; then maincontent div
bottom panel on IE7 isn't aligning as on the others. Working page is posted
here:
http://www.riskeneering.com/IndexNew.html

Started with a DW fixed header footer/3 col layout hoping to avoid errors, but
still challenged. I appreciate any help:embarrassment;