Wrap everything in a container div.
CSS
Code:
div#container {
position: absolute;
left: 50%;
margin-left: -360px;
}
Using this method, where i have 360px it should be half of the width of the div. In fact looking at that code i've forgotton to put in a width. I wonder how that works then

lol! (It should be 720px there). Note thats it's
minus half the width.
Thats the way i use, but i think the most common way is:
Code:
body
{
text-align: center;
}
div#container
{
margin-left: auto;
margin-right: auto;
width: <your-width-here>;
text-align: left;
}
It's all in the
margin-left/right: auto. The text-align: center on the body is just for old IE's that dont use the margin setting properly.
Also just to note, your container shouldnt be 800px, i think ~750px is the actual max to fit into a browser at 800x600 resolution.
EDIT: Well holy crap. Beaten by a country mile!
Did i nod off mid-post or something? rofl!