Hi Giuseppe,
thanks for the hint. Now it works again.
I summarised what I've done for future reference.
I've downloaded a 2.6.16 kernel, compiled and booted.
then I've installed NI-VISA packages with
alien --scripts <package>.rpm
dpkg -i <package>.deb
in the order listed in the NI-VISA INSTALL script
once done I launched updateNIDrives (don't know if was necessary)
then I've done the same for labview 8.2.1 packages
next: I'll try to install NI-488 and NI-DAQ
G.