Re: GeForce FX 5200 Ultra failes
run top and you will proberly see XFree86 runngin 95%+
you can kill -9 the X process and your login manager will restart it and all will be well (for a short time).
Many people are this issue, no fix but, if you disable APM and lower the AGP speed or under clock you might get a more stable system, also you could try the older 4xxx series drivers.
I just do not use games or xscreensaver and have months of X uptime