<img src="yourimage.jpg" width="150" height="200" onmouseover="this.src='yourimage.jpg';this.height=400;this.width=300" onmouseout="this.src='yourimage.jpg';this.height=200;this.width=150">
I just replaced onclick to onmouseover, and ondbclick to onmouseout. This should work, if it doesn't, just tell me.
where to place it?
It depends where you want it to show up on your site.