Risolto. Per chi fosse interessato, Il CSS diventa:

codice:
div#contenitore{
        margin: 0px auto;
        width: 720px;
        text-align: left;
}
div#menu{
        float: right;
        width: 160px;
        text-align: left;
}
div#testo{
        text-align: left;
        width: 550px;
        float: left;
}
Mentre l'HTML:
codice:
<div id="contenitore">
[img][/img]


<div id="testo">
        dsajkasdňljsdlasdjadskl sdds adsdsad adsasdasd asdsdaasd asd asd 
        dsasdasdasdasd asdad sasd dasas asd assadadsadsasdsd
    </div>
    
    <div id="menu">
        sdjsdlaksjadkldasj 2lk2jlkkjklasjdasklsa
    </div>

</div>