Trouble with Windows7 and IE 7/8 etc.

I am having problems with the way Windows and IE 7/8/FF7 are rendering a site I am building. (Look at this page: https://www.athenacare.com/blog/?page_id=78. I added the green border to the body and the red border to the content for trouble shooting purposes. #primary starts just under the header and then is the same size as the body on the L-R-and bottom.)
As you can probably see (unless you have a Mac running FF3.6, the content text is running right over the footer and below. Yet, it seems to me that more content should push the footer down. In addition, on WinXP and IE7, the layout totally falls apart.
I validated my “child” CSS and it is okay. The 20-11 style sheet showed many problem, but not with structure. HTML validation showed many problems, especially with DOCTYPE! If you look at page source, the DOCTYPE is not what I would have coded in a standard site. I know that DOCTYPE effects browser rendering.
Can any one give me some insight as to what is going wrong? I would sincerely appreciate some help on this.