Okay, I took a look at your page and the main problem I see is more fundamental than the columns. There's no reliable way to center anything in relation to anything else row-wise on your site without a "container" (or wrapper) whatever you want to call it.
I fixed this pretty simply by wrapping everything from the header to the footer in a div
with the ID of container
(like so <div id="container>"
)
It looks like the overall width of your content is 1100px so I added this CSS to the container
#container {
width: 1100px;
margin: 0 auto;
}
What this does is unifies the boundaries on each side of your layout so things can be positioned relative to this boundary.
The next error in your code is that IDs shouldn't start with a number. Nonetheless after you consider changing the name of the ID you should add the following CSS:
#threeColumns {
width: 100%;
margin: 0 auto
}
With these modifications you should be able to center your columns (and everything else you'd like to center).
These exact widths are not pixel-perfect. I am just using these to illustrate the methodology I am using.