Iam running mandrake linux 6.0. I just installed it. Now how do i changed to screen resoluion to 800x600? becasue i get these scratches on my screen every time somthing hapens !!!

make sure the X server you choose when configuring X with Xconfigurator matches your graphics card,
if it does, and you have set up multiple resolutions you could use CTRL and + or - to change resolutions.
If you didn't and you know your monitor/card can have it, edit /etc/X11/XF86Config(-4), look at the section called "Screen", the subsection "Display" where it says Modes "1024x768" "800x600" and add the resolution you want.
Be carefull, the last routine should really be done tru Xconfigurator, you are the only one responsable for *not* blowing up your stuff :-].

IS there a program that will scan my computer and list the hardware i have?

$cat /proc/pci will will display all the pci bus hardware, $cat /proc/cpuinfo for the cpu and for nvidia cards do $cat /proc/nv/card0