[CyberAlien]

Whole header is in one table, and those borders are table cellspacing, so to remove those borders you'll need to move header outside of table. Easiest solution is to put it in <caption> inside table, so code would be like this:

<table ...>
<caption>
  header text
</caption>
<tr>
  ...and the rest of table

then in css add this:

caption {
 display: block; 
 margin: 0; 
 padding: 3px; 
 ...background, color, etc... 
}

Note: this just an idea of how it can be done, not exact code.