Edit in JSFiddle

<div id="conteneur">
  <div class="bloc_gauche">
  </div>
  <div class="bloc_centre">
  </div>
  <div class="bloc_droite">
  </div>
</div>

#conteneur{
  width:315px;
  margin:0 auto;
}
.bloc_gauche{
  float:left;
  width:100px;
  height:100px;
  background-color:red;
}
.bloc_centre{
  margin:0 5px;
  float:right;
  width:100px;
  height:100px;
  background-color:red;
}
.bloc_droite{
  float:right;
  width:100px;
  height:100px;
  background-color:red;
}