It's not that your center text is overlapping the sidebox, rather the sidebox image is shifted right and covers the text. The link area is where it should be, but the image doesn't correspond... wierd.
I saw several suspicious definitions, but finally found the culprit in the betterCategories stylesheet:
.betterCategories {
font: 11px Verdana, Arial, sans-serif;
background-image: url(.../includes/templates/kakuro/images/kakuro_icon.gif);
background-repeat:none;
background-position: 0em 50%;
background-color: rgb(0,52,102);
border-top: 2px solid #ffffff;
color: #ffffff;
font-weight: bold;
line-height: 150%;
word-spacing: 2px;
margin-left: 60px; <-----------CHANGE TO 0px
text-align: left;
width: 190px;
}
I would have thought this would just squeeze the text to clear the left margin, but apparently the background kakuro_icon shifts too and carries the text with it? Doesn't seem right, but it's what happens.
On another topic, I noticed that on my 800x600 monitor the logo squashes and the center text is cut off on the right. If you set a min width for the logo wrapper, it won't squeeze past a certain point (this may not work in IE, according to the w3schools css ref page):
#logoWrapper {
min-width: 820px;