The MX400 is a fairly old card (legacy) and the newer Nvidia drivers probably don't support it.
The minimum recommended issue for the Nvidia card via the wiki used to be a 6XXX series.
The latest wiki says 6200 to 8500. http://wiki.linuxmce.org/index.php/What_hardware_I_will_need
You may be able to use a MX400 but in UI1 only.
If you are installing 710 Kubuntu for the 640x480 problem you could try useEDEID=true in xorg.conf (2 places).
If you are trying the 810 alpha, well, it may not like your graphics card.
What kind of terminal are you hooking up to? A monitor, a CRT, LCD or plasma?