Well to get rid of the gaps between each category section just remove the div off the bottom:
Code:
<div style="padding: 10px 10px 10px 10px;"></div>
However I think your forums look fine seperated the way they are now, I think you should leave the gap!
As for the large gap above the navbar, I can see what's causing it, but without seeing exactly how it's laid out in your templates I can't say for sure how to remove it. Try posting your header template, we'll see if it's in there