I used to run SoftImage 3.8SP2 on that same setup - I had an AMD K6III 450 processor machine
I was using the Detonator drivers for the graphics card, available from the Nvidia website - the drivers that came with the card weren't too hot.
Once these were installed, Soft ran pretty much trouble free
SoftImage does crash sometimes, but on a trouble free system it will resurect itself to the point of the crash, preventing loss of work. It shouldn't crash often though
If it always crashes after about the same period of time, check your Bios settings, particularly with regard to memory usage.
I found a good way to check the likely stability of the machine while running OpenGL dependant programs (like Soft) was to run the 3D Lettering screen saver - if you leave it running this over night and it's still there in the morning then your OpenGL setup is trouble free.
I'd better be workin now
Hope all this helps