[CentOS] CentOS 5 dual head doesn't work

> I just bit the bullet and installed CentOS 5 on my work desktop, and
> although I have two monitors and a card that supports them, I cannot
> get the display configuration to work with both as a continuous
> (spanning) desktop.  I have tried using the correct (autodetected)
> monitor type (digital and analog), a generic LCD with 1280x1024,
> nothing works.  Every time I set the configuration, the X server fails
> to restart and I wind up with single-head monitoring (duplicate
> displays on both screens).

What model of video card are you using?