First you will need to create your images. You will need two, one for each button.
Img on is the image that will be displayed when the page is loaded. Img off is the image that will be displayed on mouseover.
I used the Acme Label Maker to make the sample images.

Fill in the table options and enter the width and height of your images. Then enter your image urls, the url of the page and the alternative text. Click generate and copy and paste the script to the head of your document. Add the html to the body. There are comment lines included to guide you.