You do the change as root?
Don't be scared, but try changing the /etc/X11/XF86Config-4 file manually with a text editor.
You'll see a section like this:
Code:
Section "Screen"
Identifier "Screen 1"
Device "Trident"
Monitor "LCD"
# DefaultDepth 8
# DefaultDepth 16
DefaultDepth 24
# DefaultDepth 32
Subsection "Display"
Depth 8
Modes "800x600" "640x480"
EndSubsection
Subsection "Display"
Depth 16
Modes "800x600" "640x480"
EndSubsection
Subsection "Display"
Depth 24
Modes "800x600" "640x480"
EndSubsection
Subsection "Display"
Depth 32
Modes "800x600" "640x480"
EndSubsection
EndSection
Just add "1024x768" in front of the "800x600" of the default "depth" and you should be good to go
Sometimes KDE's admin functions are a bit flaky.
--Shade