I have FreeBSD running the nvidia 4365 drivers and I downloaded the UT2004 demo which works great if I run a TWM desktop
If I start KDE and then run it, I get the splash screen, then it changes resolution shows a black screen and wedges my PC solid (can't ping it from a remote host).
I have a Dell Inspiron 8600 with a GeForce FX Go5200.
Also, my Qt is built with OpenGL support. Neverwinter Nights plays fine in KDE.