<input type="button" onClick="doit()" value="Do it">

<script>
function doit() {
 drawRectangle(100, 150, 200, 100);
 myrect = document.getElementById("newdiv");
 myrect.innerHTML= myrect.innerHTML + "<h1>howto</h1>";
} 
 
function drawRectangle(left, top, width, height) {
 if (document.createElement) {
   newdiv=document.createElement("div");
   newdiv.style.position="absolute";
   newdiv.style.left = left+"px";
   newdiv.style.top  = top+"px";
   newdiv.style.width = width+"px";
   newdiv.style.height = height+"px";
   newdiv.style.backgroundColor = 'red';
   newdiv.style.visibility = 'visible';
   newdiv.id = 'newdiv';
   newdiv.innerHTML = "real";
   document.body.appendChild(newdiv);
   }
 }
</SCRIPT>