Changing the screen size at run time comes up often over VNC connections, and with Virtual Machines. A working Xrandr configuration is needed for this. The major distros are somewhat in transition so I've needed to know much more than I every wanted to make this work.
When booting CentOS in particular using a VMWare driver, this pre XrandR server has a number of video configurations that are not working, or stop working after updates.
Here is one solution that works with the 10/2010 updates.
1) Enable XRandR
yum -y install libXrandr
Option "RandR" "on"
2) Set display for 1280x800
This allows 4:3, and what appears to be a maximum login 16:9, 1280x800. Even
on a 1920x800 monitor this was the case. Likely an aspect of the vmware driver used within the VM.
(Set Both Hardware and Monitor to your maximum resolution 1280x800)
This may show the XrandR error, or let you change the display immediately. Sometimes you can get this to allow a higher resolution, but in all cases you need to have the choices to change the resolution.
In some cases, you will need this utility to change the resolution size.
2a) On Ubuntu - 10.04 too - if the display is not detected, you can't move the maximum resolution beyond 1024x768
3) Start in Runlevel 3
Having the console in mode 3 will not consume the memory for X and the graphics driver unless you choose to start it.
or if this fails:
It's a bit messy, but will eventually go away as the upstream releases are cleaning this up.