templating - how can I do this..?

To have a listing of categories in squares with 3 categories per line like that on your homepage, it's quite easy.
You don't need to edit any code.

Go in the menu manager of joomla in the "Hikashop default menus" menu and set the "categories listing" menu as 'home' menu.
Then, click on the "hikashop options" link of that menu and check the options:
number of columns -> 3
border -> yes
number of elements -> what you want per page
layout type -> div
margin -> 0px
Show sub categories -> all direct sub categories
..etc..

And voilà. You will now have a a category listing on your home page which looks roughly like the one of your link.