Old zones use BSP trees, you have to create the octree yourself (very straighforward and takes like 2 hours max. to implement fully).

When you have that octree, group the faces by texture for each leaf in the tree. After that you can easily do frustum culling against the bounding boxes of the leafs. That's almost all you need to do to get fast rendering.

Yea, it's very easy to do frustum culling using the octree. If you want, pull octree.c/octree.h from OpenEQ's source... should help you quite a bit. It's released under the GPL, btw, though I haven't yet put it in the source :P

Thanks, I had a look at your code.

The idea seems pretty simple really but your code doesn't really work with the way I've stored things so I'll probably have to re-do it myself this time.