Fulvio,
I found the answer to my problem.
My VIA Sata controller uses ahci to communicate with my Samsung 80GB SATA disk, but the ahci.ko driver was not in the lib/sata/chipsets directory of /boot/initrd.gz.
So, I copy it there from /cdrom/modules/2.6.25.9/kernel/drivers/ata, and all was ok.
Thanks a lot for your help.
Manuel