problems with css layout

i've been doing table layouts for quite some time now, but recently i started to learn how to do so with css in order to make a joomla template. Im not fully satisfied just yet becouse im having some trouble to do the layout i wish to achieve. Until now i have used float:left; and just positioned some div boxes until i got a 4 coloumn layout like the link bellow shows.

http://www.xgs-gaming.com/

But i wish to do more, maybe more like this one:

http://www.xgs-gaming.com/templates/TLT/files/layout.jpg

i tried absolute positioning but then the boxes were relative to the body, or the corner of the screen.. i would like to position relative to the parent box, (the main wrapper). Im not able to do so. Any suggestions about how i can achieve this kind of layout?

http://www.xgs-gaming.com/templates/TLT/files/layout.jpg

thanks in advance.

Start with fixing the errors in your markup, see http://validator.w3.org/check?uri=http%3A%2F%2Fwww.xgs-gaming.com%2F&charset=%28detect+automatically%29&doctype=Inline&group=0

oh my.. that many errors? how is that possible.. :(