Roving horizontal lines
I am using a pretty old monitor, which I have managed to get to work at a res. of 800x600, but I had severe problems trying to get it up to the standard 1024x768.
I discovered that my monitor did not fit the standard VESA modes set by XFree86, so I had to put in the refresh rates manually.
When I managed to find these out from the manufacturer and key them into the Monitor control panel, I found that my monitor has the 'roving horizontal lines' problem, as set out in the man page for XFree86Config (about halfway down, under the 'monitor' section).
I read that the fix for this is to manually specify a 'modeline' in /etc/X11/XF86Config, adjusting manually one of the values therein - the only problem was that when I did so, following the example given me by a previous log given by the X server, it gave me an error.
It told me that the 'virtual height' of the monitor was set to 0, when the minimum required by the monitor was '128'. I don't understand what this 'virtual height' is, and especially how on earth my setting this 'modeline' - which was all to do with horizontal and vertical refresh rates and 'dot clocks' and 'sync starts' (none of which I can either understand or find explanation for anywhere on the internet or amongst the XFree86 man pages or website) - had anything to do with it.
My distro is RHL 9 (Shrike) pretty much out of the box, if that is any help. I can't get my hands on the X server log right now, but I will happily produce it in all its 'glory' if it could be useful in solving this problem.