poloktim, first thing i would do is run 'xf86config' as root, it's a program that will write a new X config file for you.
before you do that, look for your current XF86Config file. it's probably at /etc/X11/XF86Config or /etc/X11/XF86Config-4 or /etc/XF86Config and rename it by adding .bak or .old to its name. This way you can have a look at the old file and at the new one and copy and paste any bits you like from the old one into the new one when you're finished. Also, if you duff up, you just need to rename your original XF86Config file back to its original name to get back your original configuration.