There are erros throughout your site starting at th ebeginnign of the file where you specify two character encodings. You do have some weirdness with your main navigation. There's an addition LI pair wrapping around all your LIs but the first?
Right after that you use a tag 'center'. As far as I know there is no such tag in XHTML, so that'll be doing some wacky things.
You're also using HTML 4 'br' tags rather than XHTML (your doctype). They're 'br /'
You've also wrapped font tags around soem sections of text. Font tags are also not in teh XHTML spec. You could try getting the desired effect using classes and defining them in your CSS.
Under 'Recent Entires' your first unordered list ('ul') using the clas s 'menublock' isn't closed. All tags in XHTML must have a closing pair or self close. You also at least one occasion in your main content where you double the opening 'p' tag but only close one.
You really need to use a validator and see all the errors in the page and then clean them up. Once you've done that you will have likely fixed most of your trouble spots.
Additionally, you'll have a real tutorial for your readers: Writing valid code.
XHTML validation report:http://validator.w3.org/check?verbose=1&uri=http%3A%2F%2Fdesignnewbie.com%2Fwhere-to-start%2F