Hi,
I think, what you want to do is Sectors, Portal. So it''s pretty easy.

typedef struct tagSectors
{
Polygons *Polys; // This is a list of ptrs to polygons that make this sectors
Portals *Portals; // This is a list of portal that are being a part of this sectors
Box BoundingBox; // With this, you can make a rapid check, did i''m maybe in this sector
};

So, the only thing that you have to do is check the sector you''re in, test each polys to check if you see it. Then Draw them. After that, check if you dont see any portal, when you see a portal, that mean you maybe see trought a door, a window, a hole, ... You you must check the next sectors which must be attached to the same Portal as well.

This is not very complecated to implent. But something harder to do is implement Portal with octree, this way it''s could be great.
In the case you want to use Octrees too, with your portal engine.
just replace Polygons *Polys in struct, by something like COctree Octree;

Happy Coding,
LowRad