Fullscreen with different resolutions

[julius Junghans]

Hi,

my native LCD resolution is 1400x1050, now i need 800x600 my a low end 
beamer. switching to 800x600 with Fn+Strg(Ctrl)+Alt+- works but its not 
in fullscreen
Any idea how to get fullscreen for all resolutions?

my relevant(hopefully) config lines:

Section "Screen"
    Identifier  "Screen 1"
    Device      "My Video Card"
    Monitor     "My Monitor"
    DefaultDepth 16

    Subsection "Display"
        Depth       16
        Modes       "1400x1050" "1024x768" "800x600"
    ViewPort    0 0
    EndSubsection
EndSection

Section "ServerLayout"

    Identifier  "Simple Layout"
    Screen "Screen 1"
    InputDevice "Mouse0" "CorePointer"
    InputDevice "Keyboard1" "CoreKeyboard"
EndSection


X Window System Version 7.0.0
Release Date: 21 December 2005
X Protocol Version 11, Revision 0, Release 7.0
Build Operating System:Linux 2.6.15-gentoo-r5-schleppi i686
Current Operating System: Linux schleppi 2.6.15-gentoo-r5-schleppi #1 
Tue Feb 14 15:26:42 CET 2006 i686
Build Date: 09 March 2006

Julius