Hi Piips,
I agree with Ricky here, it's coming along, and you are most definitely not a tönt: some things are more difficult than others and there is a learning curve, and what you are trying to do is not one of the most trivial things ;)
a bit difficult to see, as I can only see the results of php, but it seems you have been editing more in the plugin, because I see it's creating a class="content" within an id="content" which shouldn't exist: there should be a class="container". Look at it in firebug and you'll see -- web developer tools for firefox are very good also, as they let you mark the different 'boxes' (that's what div is, kind of a 'box') within one another, and see their relationships
some more hints:
If you check with firebug, you'll see also that this id="content" is floated to the left, and all the other 'boxes' are within it, which is why you can't move them to the center of the screen. These 'boxes' are, beginning with the outermost: content (id), container (should be class), hrz-container (id, what was the old img-container), hrz-container p (that's attributes for the p tag when within the hrz-container)
I think hrz-container is ok, the only problem being that it tries to get to the center but can't because it's squashing its nose against the right side of the content 'box'
god fortsättning ;)