We are having similar issues here. Dual Opteron, RedHat 9 Enterprise, Asus V9560 card with GeForce FX5600 GPU. Also using the 4499 drivers. X crashes, or hangs unless NvAGP is set to 0 or 2. But will definitely crash if we load glx.
Are you guys able to load glx? I really don't want to ask my boss for $$ for a new graphics card, if that is the issue.
My other thought is to configure the machine so that I can boot using 32 bit Redhat, which will hopefully allow me to get my 3-D back. At this point,
3-D is more important to me than 64-bit.
My other gripe is that installing the 4499 drivers seemed to have wiped out my glx libraries that the nv driver was using. I'd even settle for falling back to nv if I could get glx going again.