Great! CSS is something that you definitely want to have in your skill-set.
As for the design, the text on your buttons could be more readable, the separator lines are also off between the Downloads and Contact (by about 2 pixels) buttons.
If you haven't already, you might want to have some fun with hover effects on your buttons. As an example, the code here will turn your button's background white when you hover over it.
Code: Select all
.divclass:hover{
background-color: #FFF;
}
You might want to also have some fun rounding the edges of divs with
Code: Select all
.divclass{
border-radius: 5px;
-moz-border-radius: 5px;
}
that will round the div's edges by 5 px. Both lines are needed for it to work due to browser compatibility issues. A border around your main content wrapper/div might also be nice.
As Jack has pointed out, the top of the content div looks empty against the blue header, so you might want to consider bringing down the menu onto the top of the content div so it acts as a divider between the header and the content.
I can't check you code to see if it is semantically clean, but there should be much problems there on layout as such.
Otherwise, quite a good layout. If I were you though, I would polish it up a little bit more before showing your friends at Zeatnolt.

Keep it up!
pax.