As the only warning I've found in XFree log was about modclock in 1024x768, I've tryed using 800x600... same result !
My motherboard is a MSI 6533:
If I can get some usable MS-DOS bootable floppy, I'll try to update the bios (latest revisions description talk about VGA & AGP).
Last file I can attach is the installer log: here's 4363 one.
I'm also a little surprised some get helped to get root on their system, and I don't even get a thing like "I've looked at your files, found nothing, good luck since there's no hope".