While waiting for a reply, I made two changes:
1. Switch the card to GeForce Erazor X2, which the X configurator recognize as NVIDIA GeForce 256 (generic).
2. Compile from the NVIDIA kernel driver source using NVIDIA_kernel-1.0-2960.tar.gz
The outcome is essentially the same. The log file doesn't show any error (EE) message, only one warning message (WW):
(WW) NVIDIA(0): Failed to verify AGP usage
Please refer to the attachment for a full XFree86.0.log file.
I did try your recommendation, setting the "NvAGP" option to 0, 1, and 2, the problem persist.
On setting "NvAGP" to "0", the log file diff:
< (**) NVIDIA(0): Option "NvAGP" "0"
< (**) NVIDIA(0): Use of AGP disabled per request
> (WW) NVIDIA(0): Failed to verify AGP usage
On setting "NvAGP" to "2". the log file diff:
< (**) NVIDIA(0): Option "NvAGP" "2"
< (**) NVIDIA(0): Use of AGPGART requested
From the NVIDIA kernel driver source, it seems that the SiS 645 chipset is recognized, in fact it recognize up to SiS 740. But what bugs me is that my chipset is SiS 645 DX, the device id is 0x646 as oppose to 0x645 for SiS 645.