I found a solution, really not perfect but it gives me the wanted result.
First, I reset the blocking CSS attribute :
.form_text label {
*position:relative;
}
And next, to avoid having IE move my second label, I added an empty div to allow the clear (thanks JQuery) :
$('.form_text').after('<div style="clear:both;font-size:0;height:1px"/>');
I don't realy like this solution since it need JS, however, the :after
do not work on IE7 and all the css fix to replace it made the browser hang on my page ...
-- Idea based on the answer of this question : IE7 float right problems