Well. It sounds like you're misunderstanding what CSS does. It isn't content, it's just instructions for how the content should be laid out. The HTML/XHTML is the content. So, your middle section will be told to lay at such and such position with such and such attributes by the CSS, then the content of that section will be the HTML code.
To get a good understanding of how it works download one of those templates I linked to. Look at it with no content or anything, just how the CSS and HTML work together. Then, once you are familiar with that, add a menu using the same images from your ClanTemplate. If you look at my example code a few posts back then that will get you started on a menu. Once you get the menu down get your middle content set up with borders or whatever you want and then fill it with content. Just play around with it.
If it seems like too much to handle right now then you could stick with the template and just deal with the tables, but in the long run you might end up with more work on your hands.
To get a good understanding of how it works download one of those templates I linked to. Look at it with no content or anything, just how the CSS and HTML work together. Then, once you are familiar with that, add a menu using the same images from your ClanTemplate. If you look at my example code a few posts back then that will get you started on a menu. Once you get the menu down get your middle content set up with borders or whatever you want and then fill it with content. Just play around with it.
If it seems like too much to handle right now then you could stick with the template and just deal with the tables, but in the long run you might end up with more work on your hands.