zoom image from anchor links

[biju001]

like this script also. but i am seeing this zoom only work after load big size image. example i have 10 thumbnail image. each time i click thumbnail load medium format image . but when i mouse over on medium size image it will load full size and zoom function. so then no need load all full size image. and make site faster load. is that feature already in this script ? how to do

<li class="zoom">     
<a href="../image/zoom-image.jpg">
<img src="../image/medium-image.jpg" alt="" />
</a>
</li>