Problem with xcompmgr on Radeon card

[Francesco]

I have X.org 6.8.1 with this snapshot driver for radeon:
http://freedesktop.org/~fxkuehl/snapshots/radeon-20041003-linux.i386.tar.bz2
Everything works fine including tv-in and dri with 3d acceleration and I 
get about 1400 fps with glxgears.

The problems start when I run xcompmgr, it works (and glxgears continue 
to give me high FPS) but X in general is very slow, unusable. I have 
read of other people in the internet with problems with ati cards and 
x.org 6.8.1, but here everything works except xcompmgr (same behaviour 
with metacity patch to enable composition manager).

When I launch X I noticed this line:
(WW) RADEON(0): Failed to set up write-combining range 
(0xe0000000,0x4000000)
I think that can be related with my problem.

Any hint to solve this?
Thanks.
Frankk