Ya, X -configure basically configure ur xorg.conf with a available video driver. If the exact video driver is not present, vesa driver will b loaded
X -configure will create a xorg.conf.new in your root directory and if u open it, u can seen the driver used for video card.
Driver "<your driver name>"
copy this xorg.conf.new file to /etc/X11/xorg.conf.
try restarting the X,
If this is not sounding good,
Try replacing the driver "<your driver name>" with "vesa"
vesa is a basic and generic driver which suits for all video cards and u will not get a higher resolution.
U should probably find a corresponding video driver and install it and then replace the driver section with the required one if u need a higher resolution.