I've reached the end...
It's just about over for me now.
My RH9 PC is locking up 1-2 times per day and has become "unreliable" - unheard of in Linux circles! ;-)
I have sent a few emails to the nVidia support address but they've never responded so I can only assume that they just don't care. Making too much money from Windows I guess.
I can use my FX5600 in another Windows PC and I'll go back to something that has better Linux support.
I'll still keep in touch with the situation, but I just have too much work to do to wait in hope for a fix to magically appear.
The most annoying thing is that nVidia has a reputation for offering good Linux support, but from what I have seen their support is hopeless. You can't even get a response out of them.