(UT is a fun game!)
Anyway, I had the experience with my GeForce2 GTS that OpenGL worked better than D3D. Then Switched to a GeForce3 (not Ti) and couldn't tell any significant difference between OpenGL and D3D (I have Hi-res extras installed and run with everything enabled). Then I switched to WindowsXP and now the D3D is looking better than the OpenGL (probably DirectX 8.1 doing this)
Anyway, you should see a BIG improvement going from TNT2 to a GeForce3 (any). I suggest using display properties and changing your video adapter to Standard PCI adapter (VGA). then go to control panel and uninstall any utilities associated with your video card if they are left over from the manufacturer stuff before you went to detonator drivers.
then go to
here and download the detonator destroyer and use it according to instructions. Then re-install your detonator drivers and see if this helps
It sounds like you may have some old driver stufforz lurking around
Good Luck!