6600 + Via Chipset -> most games unplayable
I have a GeForce 6600 AGP running on an Athlon XP 1800+ with a VIA KT266 motherboard and 512 MB of RAM. Most DirectX games I tried are unplayable due to vertex coordinates corruption. OpenGL games work fine both in Windows XP SP2 and Linux. My own DirectX and OpenGL code works just fine (fixed function pipeline, not vertex shaders). I therefore doubt this is a hardware problem.
I've installed the latest nVidia drivers, the latest (and previous version) VIA drivers including the AGP drivers, I tried RivaTuner to disable most advanced features, I disabled combined writes in the Control Panel. Nothing works. I get exactly the same horrible artifacts.
Battlefield 2 and Halo exhibit this behavior (and are unplayable). Hitman 2 and Joint Ops work fine.
I know for a fact I'm far from the only person having this problem with a 6600. Is there an official solution provided from nVidia that actually works? Do we have to accept that nVidia has just abandoned owners of certain nVidia products considered "too old" to be worth supporting?