X Resolution

/etc/X11/XF86Config

А что именно редактировать не можешь написать?

пускаешь XFree86 -config, потом доводишь полученный конфиг до ума руками смотря в чужие конфиги

PS: хотел конечно сказать:
XFree86 -configure
Вот скажем мой конфиг, обрати внимание на DefaultDepth:


Section "ServerLayout"
Identifier "XFree86 Configured"
Screen 0 "Screen0" 0 0
InputDevice "Mouse0" "CorePointer"
InputDevice "Keyboard0" "CoreKeyboard"
EndSection

Section "Files"
RgbPath "/usr/X11R6/lib/X11/rgb"
ModulePath "/usr/X11R6/lib/modules"
FontPath "/usr/share/fonts/truetype"
FontPath "/usr/lib/X11/fonts/cyrillic"
FontPath "/usr/lib/X11/fonts/win"
FontPath "/usr/lib/X11/fonts/misc"
FontPath "/usr/lib/X11/fonts/100dpi/:unscaled"
FontPath "/usr/lib/X11/fonts/75dpi/:unscaled"
FontPath "/usr/lib/X11/fonts/Type1"
FontPath "/usr/lib/X11/fonts/Speedo"
FontPath "/usr/lib/X11/fonts/100dpi"
FontPath "/usr/lib/X11/fonts/75dpi"
EndSection


Section "Module"
Load "glx"
Load "record"
Load "extmod"
Load "dbe"
# Load "dri"
Load "xtrap"
Load "type1"
Load "speedo"
EndSection

Section "InputDevice"
Identifier "Keyboard0"
Driver "keyboard"
Option "AutoRepeat" "500 30"
Option "CoreKeyboard"
Option "Protocol" "Standard"
Option "XkbKeyCodes" "xfree86"
Option "XkbRules" "xfree86"
Option "XkbModel" "pc104"
Option "XkbLayout" "ru"
Option "XkbVariant" "winkeys"
Option "XkbOptions" "grp:ctrl_shift_toggle,ctrl:ctrl_aa,grp_led:scroll"
EndSection

Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "ImPS/2"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "true"
Option "ZAxisMapping" "4 5"
EndSection


Section "Monitor"
Identifier "Monitor0"
VendorName "MEL"
ModelName "DPRO750SB"
HorizSync 30.0 - 96.0
VertRefresh 50.0 - 160.0
Modeline "1024x768" 121.60 1024 1068 1116 1344 768 798 814 833
EndSection


Section "Device"
Identifier "Card0"
# Driver "nvidia"
Driver "nv"
VendorName "NVidia"
BoardName "GeForce2 GTS/Pro"
BusID "PCI:3:0:0"
EndSection

Section "Screen"
Identifier "Screen0"
Device "Card0"
Monitor "Monitor0"
DefaultDepth 24
SubSection "Display"
Depth 1
EndSubSection
SubSection "Display"
Depth 4
EndSubSection
SubSection "Display"
Depth 8
EndSubSection
SubSection "Display"
Depth 15
EndSubSection
SubSection "Display"
Depth 16
EndSubSection
SubSection "Display"
Depth 24
Modes "1024x768" "800x600" "640x480"
EndSubSection
EndSection

xrandr - менять резолюшен на лету