The XFree86 server allows users to configure their video subsystem and thus encourages best use of existing hardware. This document is intended to help you learn how to generate your own timing numbers to make optimum use of your video card and monitor.
We'll present a method for getting something that works, and then show you how you can experiment starting from that base to develop settings that optimize for your taste.
If you already have a mode that almost works (in particular, if one of predefined VESA modes gives you a stable display but one that's displaced right or left, or too small, or too large) you can go straight to the section on Fixing Problems with the Image. This will enlighten you on ways to tweak the timing numbers to achieve particular effects.
Don't assume that you need to get all the way into mode tuning just because your X comes up with a scrambled display first time after installation; it may be that most of the factory mode lines are OK and you just happened to default to one that doesn't fit your hardware. Instead, cycle through all your installed modes with CTRL-ALT-KP+. If some of the modes look OK, try commenting out all but a 640x480 and check that that mode works. If it does then uncomment a couple of other modes, e.g. an 800x600 and a 1024x768 at a frequency that your monitor should be able to handle.
More help is on the way. Many driver modules in the just-released XFree86 4.0 support DDC, the VESA Display Data Channel facility. When DDC is enabled, the monitor actually tells XFree86 what modelines it can support. So with 4.0 and any recently-manufactured monitor you are likely not to have to do any configuration at all.