Make Wiki landing page just display Categories / Wiki titles

How can i make the default landing page of /wiki stop displaying the posts of Wiki's.
Then make it display a list of Wiki titles ( with links to the pages ) under each Category

So you would end up with something like below:

Help --- Category title
how to get help. --- Wiki page
About help --- Wiki page

Test ---- Category
Blahblah --- Wiki page

I know its possible , just how ?

Thanx in advance,
Justine