The way you designed this means it is not flexible, you can’t just create new categories in EE and it will then automatically create a new button. So the buttons will have to be hardcoded. You make a category, or a weblog and use that URL as a link.
Two options:
1: Use good old HTML and make an image hotspot. In Dreamweaver this is done easily. It generates something like this:
your image
<map name="Map" id="Map"><area shape="rect" coords="155,106,407,292" href="#" ></map>
2: Make a small DIV layer on top of this image with the buttons area cropped in it and link that image. You can then also make a rollover, using #div:hover, where div is replaced by the name of the layer. If you place the highlight image in that div, it will be shown when you roll over this button. This rollover does not work for IE6 and below, but let’s hope that it will become extinct ASAP. (In holland it is now down to 25%)
You could also use JAVAscript, but that is way to complicated IMHO.
Hope this all makes any sense!