Changing to different video card properly

[Barry Yu]

FC6 - Every time I changed from a video card to a different one I always 
got problem mainly the X server won't start, when removed xorg.conf 
filel and restartx sometimes it will auto detect the new card but not 
every time.
What is the the proper procedure to switch to a new video card? 
Especially the new one is a dual head ATI X1300 chip.
What is the difference between X -config and system-config-display