Well, I tried disabling OS PnP and assign IRQ to VGA on Bios. I tried to remove rivafb from my kernel (Mandrake 9.1), but unsuccessfully.
I will try also the AGP option mentioned by you, and this will be my last attempt (or I will change the video card).
Anyhow I would like to know if there's somebody with my exact hw configuration who was able to complete the installation succesfully.
Thanks, I will let you know about my progress.