Before you try anything else, remove the duplicated opening tag for the head element.
Validators aren't as clever as browsers, but they can help. This is what HTML Tidy has to say about your homepage:
Clean that lot up and let's see the result...
ps
It's a good idea to be consistent in using either upper or lower case when creating html documents.
Browsers couldn't care less, you can even mix it up, just for fun...
This is about developing your own style of authoring, fine-tuning your code to make it easy to scan & find errors such as this.
There's a few techniques to center-align the whole document.
You could always
try nesting your page in a frameset nested in a frameset, as seen at Graphic Guru
IrfanView, who defines the width of his content frame and leaves it up to the browser to ensure the left/right frames are the same width.
All
too hard for me, & even
firefox can't bookmark the inside pages.
Here's one of my all-time favourite style snippets:
Good Luck!