Default configuration file for X server?

[Hrishikesh Murali <fnkygy@gmail.com>]

Hi,
I am Hrishikesh Murali, a new member to this list. I have debian
installed as a virtual machine on my laptop having resolution
1280x800, and by default without any graphics driver it uses a
built-in configuration for the X session.
This is a snippet from my log file :

<snipped>
(==) --- Start of built-in configuration ---
       Section "Device"
               Identifier      "Builtin Default vesa Device 0"
               Driver  "vesa"
       EndSection
       Section "Screen"
               Identifier      "Builtin Default vesa Screen 0"
               Device  "Builtin Default vesa Device 0"
       EndSection
       Section "Device"
               Identifier      "Builtin Default fbdev Device 0"
               Driver  "fbdev"
       EndSection
       Section "Screen"
               Identifier      "Builtin Default fbdev Screen 0"
               Device  "Builtin Default fbdev Device 0"
       EndSection
       Section "ServerLayout"
               Identifier      "Builtin Default Layout"
               Screen  "Builtin Default vesa Screen 0"
               Screen  "Builtin Default fbdev Screen 0"
       EndSection
(==) --- End of built-in configuration ---
<snipped>

My questions are:
1) Where is this default configuration specified?
2) There are three screens specified in the log, which one is used by default?

The default resolution of my screen in my debain VM is 1280x1024, but
my laptop resolution is 1280x800. I am not able to view the desktop
properly in my VM. Any suggestions are welcome.

--
Cheers,
Hrishikesh Murali