4
If you can find it, the Redhat theme uses a horizontal navigation bar with no left column. I was able to put together a site using that theme that had no side columns at all.
I'll check my collection and see if I still have it.
Edit: Ah, here we go... right in the themes repository.
http://prdownloads.sourceforge.net/xoops/xoops2-thm_red_hat.zip?download