The only actual conflict there is in the margin. It is defined three different times, and the last is what controls:
Code:
#mainWrapper {

	background-color: #FFFFFF;

	text-align: center;

	margin-left: 10em;

	width: 900px;

	vertical-align: top;

	}

	
...
	

#mainWrapper {background-image: none;

              padding: 0;

			  margin: 0;}



#navColumnOneWrapper, #navColumnTwoWrapper, #mainWrapper {

	margin: auto;

	}
For simplicity and sanity you should gather all #mainWrapper declarations in one rule.