kde>ctrl center>peripherals>display doesn't work: d

[dgr72371]

hello,
I just installed Knoppix on the hard drive of a laptop (looks like I'm using Debian now because of the hd install), and I've gotten it booted into KDE successfully, but the screen resolution is too big (I think it's 640x480). I remember when going through the steps of the install, it asked for me to check off the possible screen resolutions the laptop supported and I checked off both 640x480 & 800x600. I need to change it to 800x600, but when I go into the KDE control center > Peripherals > display, the mouse icon (which is an X) just spins/thinks for several seconds, then no screen comes up for me to change the resolution from. Could someone please help me with the steps I need to follow to get the screen resolution from 640x480 to 800x600. Thank you in advance!

[abouzeis]

You have to be logged in as root. Or I think you can su xdisplay * not sure though. Just log in as root --easiest.

[dgr72371]

Thanks for the assistance.
When you say "su xdisplay *", do I open up a terminal box while logged into KDE under a user name (not root) and enter this command or do something different? And what happens when I enter su xdisplay * ?