I've never had problems with the nvidia driver
either, until I
used the realtime kernel (2.6.20-rt8) and the MX4000. The latest
nvidia driver doesn't support this chipset. There is a patch for
the rt kernel and the nvidia v9631 drivers (the last version to
support the MX4000) but I couldn't get it to work (I didn't have
time to try very hard, though.)
To compile the driver, one needs to either restore the
"transitional" #define SA_.... stuff to interrupts.h (the rt8
patch had no business removing them!) or apply a patch to the
extracted nvidia sources and then compile that.
What rt8 kernel patch are you referring to and where does one get
it?