Well the most basic way of doing it would be to put an image element inside an anchor element.
<a href="the address the link should point to"><img alt="what this image is for" src="the web address of the image you want to use"></a>
Just put the address the link should point to in the href attribute of the "a" element, a text equivelant of the image in the alt attribute of the img element and the web address of the image in the src attribute of the img element.
On the page you pointed to, the buy-it-now/make-a-bid button uses
for a href attribute value. This just makes the button activate the default bid/buy button at the top of all ebay auction pages. The others just use plain adresses you change manually. Just use the same addresses that the page you linked shows, but just edit the item number to be the item number for the item on the page.
Though don't you think these buttons are rather pointless? They're already on the page anyway.