In your other topics you already had suggestions about RHEL 6 here is nice place for that. New xorg servers are so much better with auto-configuration etc.
But it is not big problem with old. All you have to do is to edit xorg.conf file for your needs:
(this link is outdated for modern distros, no need to edit that file at all, but for Red hat 5 should be OK).
I use red hat linux es 5 I use startx to start the x-win desktop. But when I use vritual manager . The display application is too large so the bottom part for the application cannot show out. I cannot scroll down to get the display of bottm part . So, I do not know what button display at the bottom part. So, what can I do . I already set the display to 800x640 already. Please advice