Particuls and depthbuffer

Hello,
I have a problem when I draw my particuls:

If I Disable the depthtest the particuls
are always drawn, although an objet can
be hide them
But If I enable the depthtest we see
the black part of the bitmap I use for
my particuls

How can we make a color not write in the
depthbuffer or
How can we use the depthbuffer in a
“read only” mode ???

thanks
GrenouYe

glDepthMask(GL_FALSE);
–render particles
glDepthMask(GL_TRUE);

thank you
!!!