I am running Mandrake 9.1 on a P3 AMD 900, Asus board, TNT2 (32mb) card with more than ample RAM etc... and was getting a freeze every day - the full hard lock up that only hitting the power switch would fix. It would die either with or without any user input !!!
Dont know if this is going to help you, but I have turned off all the advance power managment systems in my BIOS, disabled DPMS in my XF86Config file (for a screensaver I just go to a blank screen) and opted at the moment for the "NvAgp" "1" option to see how things go.
I have installed the latest drivers from Nvidia and so far the machine has been up and running 2 days without a hiccup.
Ammendum: I locked up again
so I went for the NvAgp=3 option and have allocated memory to the card with a "mem=320M" in lilo.conf this pulls the top 64mb from my total RAM and so the card can have some memory to play with. It probably more than it needs but since I have plenty to spare I gave it twice the card RAM ..... so far so good - almost 3 days uptime without a glitch.
I may lack technical expertise but brute force and persistence will win the day !!
Be warned its early days for me and I am in the process of covering all bases before I consider I have bad RAM/CPU/Mobo and need to replace them .... going for all the non cost options at the moment
I may have cured my problem, I am feeling quietly confident at this stage ..... uptime: 05:14:10 up 6 days, 7:34, 2 users, load average: 0.00, 0.00, 0.00