Margin problem

Hi, I have a problem with margin as you can view in my attachment.

I use this structure

div#container{
background: White url(../images/varie/sfondo_container.gif) repeat-y;
width:750px;
\width:760px;
w\idth:750px;

text-align:left;
}

div#navigazione{
float:left;
width:160px;
\width:170px;
w\idth:160px;
background-color: White;
padding-top:20px;
}

div#content{
margin: 0px 4px 0px 180px;
background-color: White;
padding:4px 4px 4px 6px;
}

div#footer{
clear:both;
background-color: White;
border-top: 1px dotted #EEE;
}

why???

thksss