@ pinouchon; for this type of layout you can use css3 column-count property
for this.
CSS:
div#multicolumn1 {
-moz-column-count: 2;
-moz-column-gap: 10px;
-webkit-column-count: 2;
-webkit-column-gap: 10px;
column-count: 2;
column-gap: 10px;
}
Check my example here for more How to stack divs from top to bottom in CSS
read this article for more http://www.quirksmode.org/css/multicolumn.html