This gap is created by 2 smaller gaps. The first one is due to the use of a <br />. In your tpl_header.php file, find the close table tag after <table id="Table_01" width="748" height="208" cellspacing="0" cellpadding="0" border="0">. There is a <br /> just after this </table>. Remove this.

Secondly, at the very end of yuor stylesheet, add:
Code:
.centerColumn {
  padding-top:0px;
}
Also, on line 1135 of your stylesheet, change the
Code:
.leftBoxContainer, .rightBoxContainer {stylesheet.css (line 1135)
border:1px solid #727D84;
margin:1.2em 0em 0em;
}
TO:

Code:
.leftBoxContainer, .rightBoxContainer {stylesheet.css (line 1135)
border:1px solid #727D84;
margin:0em 0em 1.2em;
}
THis will remove the top padding/margin from the columns, and in teh case of the sideboxes, move the margin from above each box to below each box.

Absolute