check out page display/layout problem

[PiscesFish]

When I test the check out process on my site the right part of the page disappears or over extends the the div. So far all the others pages such as product display etc. are fine. I looked for CSS specific to the width??? I hadn't changed any widths to my knowledge. Any help is appreciated. Thanks.
http://www.sitemagicdesigns.com/zen/

[Marg]

How about a test login/pass?
Marg

[PiscesFish]

Thanks for your help!
I changed the .centerColmun CSS to 600px and it works great now.

.centerColumn{
width:600px;
}