vnc'ing into the main display, using libvnc extension module seems to corrupt screen memory. This machine is on FC6, nightly patched. Very few, if any, non-fedora repos used. Graphics is Intel i810. Random occurrences, always same are of the screen. Sometimes it's there, sometimes is not, even on successive invocations. I'll attach images of the display, the xorg.conf used and the Xorg.0.log at the time.
Created attachment 156350 [details] corrupted display
Created attachment 156351 [details] xorg.conf
Created attachment 156352 [details] Xorg.0.log
Fedora Core 6 is no longer supported, could you please reproduce this with the updated version of the currently supported distribution (Fedora 7, 8, or Rawhide)? If this issue turns out to still be reproducible, please let us know in this bug report. If after a month's time we have not heard back from you, we will have to close this bug as CANTFIX. Setting status to NEEDINFO, and awaiting information from the reporter. [This is mass-filed message to all open Fedora Core 6 bugs related to Xorg or Gecko. If you see any other reason, why this bug shouldn't be closed, please, comment on it here.]
Can't replicate with F8+updates. Can't pinpoint when it disappeared, but probably in late F7+updates.
I had the same problem as you, added the following line to the Device section of my xorg.conf, and the corruption went away: Option "LinearAlloc" "16384"