And one more thing. If you want a really easy way out, you can boot your pc with a debian based live CD like Knoppix, Morphix, Mepis, Overclockix, Kanotix, etc. It will auto detect your monitor and configure xfree86. If you boot up and the display is how you like it, you can just copy that configuration to your hard drive:
Code:
mount /dev/hdaX /mnt/hdaX
cp /etc/X11/XF86Config-4 /mnt/hdaX/etc/X11/
Where the X in "hdaX" referes to the number of the root partition of your Debian installation.