Inside my wordpress theme at http://www.iam-us.nl/over-i-am-us I can not align my image left. I've added individuals WordPress Produced Classes towards the css

/******************************************
* Align box
******************************************/

img.centered, .aligncenter, div.aligncenter {
display: block;
margin-left: auto;
margin-right: auto;
}

img.alignright {
padding: 4px;
margin: 0 0 2px 7px;
display: inline;
}

img.alignleft {
padding: 4px;
margin: 0 7px 2px 0;
display: inline;
}

.alignright {
float: right;
}

.alignleft {
float: left;
}

But in some way the css isn't read well.
After I open firebug there's no class put into the image whatsoever.
Any help could be realy appreciated.

I checked all of your style.css and located that you've a bad comment here:

/** Coin Slider HACK by aSeptik *  14/06/2011 16.37.38 *  fix navigation button z-index */
#slider {
    margin: 0 0 10px 0;
    padding: 0;
    width: 950px;
    height: 350px;
    /*background-image: url('http://www.iam-us.nl/wp-content/themes/iamus/images/De-mens-op-de-juiste-plek.png');
}*/

you said the last curly brace!!

so change it out for this:

    height: 350px;
    /*background-image: url('http://www.iam-us.nl/wp-content/themes/iamus/images/De-mens-op-de-juiste-plek.png');*/
}

and that is it