There are some new NVIDIA detonator drivers that will work with tnT, TnT2, Ultra TnT2, and Vanta.
I just installed the new 1.73 drivers on my STB v4400 and they made a nice improvement. My 3DMark99 Max went from 4050 to 4165, and Quake2 gained about 1.5 fps in the crusher.dm2 demo. My DVD movies seem a little more crisp and detailed (ATI 3.1 player). To sum it up the visual quality has improved, as well as the overall speed in direct 3d / openGL.
I tried the Ultra TnT2 but they didn't seem to work as well as the TnT ones.
Come back and post your thoughts here after you install the drivers