For anyone who has had problems getting X to start on old Laptops using the SiliconMotion series of graphics cards.
For some odd reason the graphics card is poorly supported, and upon starting X you are presented with a black screen, when using the vesa driver, OR the siliconmotion driver!
In earlier versions of Linux the driver "siliconmotion" would sometimes work, depending on the version of XFree or Xorg, but logging out of X would also cause the black screen. In some distros even the framebuffer wouldnt talk to the card properly, and text mode video modes only could be used!
Fortunately the framebuffer works fine with this card in BT4.
The Fix For Backtrack 4 is to use xorg.conf-vesa as a template, and replace the driver with "fbdev" instead of "vesa". So do:
cp xorg.conf-vesa xorg.conf
page down to the graphics device section and change:
(if you use a screen that only does 800x600, delete "1024x768" from the available modes further down the page)
Save and quit, then startx.
Using the driver fbdev, may well work for other odd cards, with similar quirks.