I had this problem with 5.1 as well - I had a perfectly
working xserver on my winbook XL (uses XF86SVGA X server) I
was able to do 16bpp@1024x768 just fine, but the newer
versions of this display server don't do it. They error out.
with an error message to the effect that the display server
doesn't support the particular resolution. When I remove the
new display server and downgrade to the XF86SVGA server for
redhat 5.0, it works just fine - using the same
ps. the video chipset is Chips and Technology 65554 w/2048 video ram.
Have you tried building a new XF86Config configuration file with the
new server ? I am running in 1024x768@16bpp as I type now...