@Daniele
Copy the file Picasso96Settings### from the Picasso96 archive, found in the devs drawer, to the devs drawer on your SYS drive. Reboot, and try again. Copy the file with the refresh rates prefered, and rename it to Picasso96Settings (ie, remove the digits). I'd start with 31 or 38 if I were you.
The specific tooltype in the monitor driver should point to devs:Picasso96Settings.
-EDIT-
As mentioned in other posts; if the Voodoo card isn't recognised by PCIInfo, then you will never be able to get it up and running.