d2z's blog

The term rollover in this regard originates from the visual process of "rolling the mouse cursor over the button" causing the button to react.

Rollovers can be done by imagery, text or buttons. The user only requires 2 images/buttons (with the possible addition of "alt" text to these images) to perform this interactive action. Rollover imagery can be done either by a program with a built-in tool or script coding..continue read here

here's an example:

rollover mouse to see the effect.

<a href="http://d2zack.blogspot.com"
onmouseout="document.images['s1a'].src='image1.jpg';"
onmouseover="document.images['s1a'].src='image2.jpg';">
<img alt="" border="0" name="s1a" src="image1.jpg" />
</a>

here is what the code is about. correct me if i'm wrong. kinda forgot about html. :-\

First line:
the first line is the link for the picture if you click the rollover image. you can put the link there.

Secone line:
the image when the mouse is not on the image

Third line:
the image when the mouse is on the image or over the image

Fourth line: the image when the mouse is not on the image

that's it. copy the code, and replace image1.jpg and image2.jpg with your image link.

ps: i'd used this before for canon 70-200mm f/2.8L IS II USM post