as first, if u just want to release a design, dont call the file extentions ".php".
infact, nobody will use your index.php like u do. programmers are setting up N-TIER models, so the index is rly just an index and doesnt hold information. (GUI, business (service) layer and data access layer are class groups).
So if you concentrade on designing a page, just use html and css files. a good coder starts with a huge conception instead of extending your php files.
secondly, if u want to use floating, its not hard to do so. there are many ways of doing it. as first u need a container that starts below the nav and stops before the footer. now u can make 3 divs in it.
Code:
<div id="content"><div id="left">left side</div><div id="center">center</div><div id="clear"></div></div>
now its important u understand that u should float every div to left in the content div, BUT the clear div. this only works if u have a fixed width (so its perfect here).
Code:
#content
{
width: 970px;
}
#left, #center
{
float: left;
}
#left
{
width: 300px;
}
#center
{
width: 670px;
}
by floating these elements to left u will have the problem the parent div wont increase the height by its content.
for that we got a final div in the container which makes sure, the height will increase of the parent div by simply clear the floats.
Code:
#clear
{
clear: both;
}
other ways are u could just float the left div, and remove the center div, and simply give the parent #container div padding-left like the width of the left div, but i prefer this kind of way.
if u still got more questions, there is no need to add anybody, just google for container tutorials in css.