hi, how to stop unwanted gdm program such as sound controller?

[shiyao ma]

Hi, buddy
     I now use Fedora 15 xfce4 spin. What puzzled me is that when the system
boots, I see logs like starting gdm3..Does that mean in this spin, xfce4 is
only a session based on gdm?
what puzzled me more is when I start a virtualmachine in virtualbox, a gdm
system setting of sound controller will appear on my host system. It seems
that the xfce4 sound controller and gdm sound controller clutters.
So, what's the method to use a pure xfce4 or how to settle down the above
problems.

Thanks.