Forum Linux.mandriva bureau plus grand que l'ecran

bonjours a tous
depuis son instalation ma mandriva 2006 m'affiche un bureau bien plus grand que la taille de l'ecran dont la definision n'est modifiable que en 640X480 ou en 800X600 (dans configuration KDE-Periferique-ecran)alors que dans configuration de mon ordinateur-materiel-ecran la j'ai toute les definisions posibles.
Mon ecran est un hitachi CM615 il est quant as luis bloqué sur 640X480 60hrz et n'en change pas meme si l'ont change la definision par les parametres expliqué au debut du post
la carte graphique est une S3 UNICHROME
apres avoir fouillé un peut partout sur le net est sur ce forum j'ai trouver des pistes en modifiant le xorg.conf mais toute ses manipulation sont restés vaine.je vous fait une copie de ce fichier dont je pense que vienne tous mes soucis.
merci de votre aide


# File generated by XFdrake.

# **********************************************************************
# Refer to the XF86Config man page for details about the format of
# this file.
# **********************************************************************

Section "Files"
# Multiple FontPath entries are allowed (they are concatenated together)
# By default, Mandrake 6.0 and later now use a font server independent of
# the X server to render fonts.
FontPath "unix/:-1"
EndSection

Section "ServerFlags"
#DontZap # disable (server abort)
#DontZoom # disable <KP_+>/<KP_-> (resolution switching)
AllowMouseOpenFail # allows the server to start up even if the mouse does not work
EndSection

Section "Module"
Load "dbe" # Double-Buffering Extension
Load "v4l" # Video for Linux
Load "extmod"
Load "type1"
Load "freetype"
Load "glx" # 3D layer
Load "dri" # direct rendering
EndSection

Section "InputDevice"
Identifier "Keyboard1"
Driver "keyboard"
Option "XkbModel" "pc105"
Option "XkbLayout" "fr"
Option "XkbOptions" "compose:rwin"
EndSection

Section "InputDevice"
Identifier "Mouse1"
Driver "mouse"
Option "Protocol" "ExplorerPS/2"
Option "Device" "/dev/mouse"
Option "ZAxisMapping" "6 7"
EndSection

Section "Monitor"
Identifier "monitor1"
HorizSync 31-70
VertRefresh 50-99

# TV fullscreen mode or DVD fullscreen output.
# 768x576 @ 79 Hz, 50 kHz hsync
ModeLine "1000x768" 50.00 768 832 846 1000 576 590 595 630

# 768x576 @ 100 Hz, 61.6 kHz hsync
ModeLine "1024x768" 63.07 768 800 960 1024 576 578 590 616
EndSection

Section "Device"
Identifier "device1"
VendorName "VIA Technologies Inc"
BoardName "S3 UniChrome"
Driver "via"
Option "DPMS"
EndSection

Section "Screen"
Identifier "screen1"
Device "device1"
Monitor "monitor1"
DefaultColorDepth 24

Subsection "Display"
Depth 8
Virtual 800 600
EndSubsection

Subsection "Display"
Depth 15
Virtual 800 600
EndSubsection

Subsection "Display"
Depth 16
Virtual 800 600
EndSubsection

Subsection "Display"
Depth 24
Virtual 800 600
EndSubsection
EndSection

Section "ServerLayout"
Identifier "layout1"
InputDevice "Keyboard1" "CoreKeyboard"
InputDevice "Mouse1" "CorePointer"
Screen "screen1"
EndSection