Già provato con il file di configurazione del pc che non fa i capricci...

Siccome mi reputo una persona pratica... ho installato mandriva e mi sono ricopiato il file di configurazione di xorg... Naturalmente l'ho modificato, non mi andava di installare moduli aggiuntivi del kernel o il driver nvidia-glx... non faccio il grafico quindi anche il driver nv può adempiere egregiamente il suo dovere...

Stranamente su un pc il driver nv lo attiva in automatico, come da seguito vi elenco il file xorg.conf:

# xorg.conf (X.Org X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the xorg.conf manual page.
# (Type "man xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
#   sudo dpkg-reconfigure -phigh xserver-xorg

Section "InputDevice"
    Identifier    "Generic Keyboard"
    Driver        "kbd"
    Option        "XkbRules"    "xorg"
    Option        "XkbModel"    "pc105"
    Option        "XkbLayout"    "it"
EndSection

Section "InputDevice"
    Identifier    "Configured Mouse"
    Driver        "mouse"
EndSection

Section "Device"
    Identifier    "Configured Video Device"
EndSection

Section "Monitor"
    Identifier    "Configured Monitor"
EndSection

Section "Screen"
    Identifier    "Default Screen"
    Monitor        "Configured Monitor"
EndSection

Mentre qui non ho avuto problemi di nessun tipo... sull'altro pc il dramma nel dramma...
Ecco il file xorg.conf dedotto da Mandriva 2010.0 sul pc incriminato, e adattato a Debian Lenny:

# xorg.conf (X.Org X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the xorg.conf manual page.
# (Type "man xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
#   sudo dpkg-reconfigure -phigh xserver-xorg

Section "InputDevice"
    Identifier    "Generic Keyboard"
    Driver        "kbd"
    Option        "XkbRules"    "xorg"
    Option        "XkbModel"    "pc105"
    Option        "XkbLayout"    "it"
EndSection

Section "InputDevice"
    Identifier    "Configured Mouse"
    Driver        "mouse"
EndSection

Section "ServerFlags"
    Option "DontZap" "False" # disable (server abort)
    #DontZoom # disable / (resolution switching)
    AllowMouseOpenFail # allows the server to start up even if the mouse does not work
EndSection

Section "Module"
    Disable "dri"
    Load "dbe" # Double-Buffering Extension
    Load "v4l" # Video for Linux
    Load "extmod"
    Load "glx" # 3D layer
EndSection

Section "Monitor"
    Identifier "monitor1"
    VendorName "Generic"
    ModelName "1024x768 @ 60 Hz"
    HorizSync 31.5-48.0
    VertRefresh 50.0-70.0
    
    # TV fullscreen mode or DVD fullscreen output.
    # 768x576 @ 79 Hz, 50 kHz hsync
    ModeLine "768x576"     50.00  768  832  846 1000   576  590  595  630
    
    # 768x576 @ 100 Hz, 61.6 kHz hsync
    ModeLine "768x576"     63.07  768  800  960 1024   576  578  590  616
EndSection

Section "Device"
    Identifier "device1"
    VendorName "nVidia Corporation"
    BoardName "NVIDIA GeForce FX series"
    Driver "nv"
    Option "DPMS"
    Option "DynamicTwinView" "false"
    Option "AddARGBGLXVisuals"
EndSection

Section "Screen"
    Identifier "screen1"
    Device "device1"
    Monitor "monitor1"
    DefaultColorDepth 24
    
    Subsection "Display"
        Depth 8
        Modes "1024x768" "832x624" "800x600" "640x480" "480x360" "320x240"
    EndSubsection
    
    Subsection "Display"
        Depth 15
        Modes "1024x768" "832x624" "800x600" "640x480" "480x360" "320x240"
    EndSubsection
    
    Subsection "Display"
        Depth 16
        Modes "1024x768" "832x624" "800x600" "640x480" "480x360" "320x240"
    EndSubsection
    
    Subsection "Display"
        Depth 24
        Modes "1024x768" "832x624" "800x600" "640x480" "480x360" "320x240"
    EndSubsection
EndSection

Section "ServerLayout"
    Identifier "layout1"
    Screen "screen1"
EndSection

Grazie lo stesso... se non avessi letto la tua risposta, che mi ha illuminato, starei ancora barcollando nel buio.
A presto.