i did the things described in this forum, including
* backup my /usr/lib/xorg/modules (using xorg 7.1 the ati_drv.so and atimisc_drv.so compiled by the following packages does not work)
* installing common-20060403-linux.i386 as described
* install the patch "ati_pcigart.zip" as described
* installing mach64-20060403-linux.i386 as described
* trying several xorg-confs.
after that, i still got direct rendering=no
from http://www.bsdforen.de/archive/index.php/t-15135.html i got the hint for using atigetsysteminfo.sh - it summarizes some "cat proc" ..
and reported that the /etc/driconf is missing. i simply installed the following driconf and got my "direct rendering=yes" and much faster glxgears-visuals.
(now i'm working to get a usable googleearth... it still is as slow as before...)
<device screen="0" driver="radeon">
<option name="vblank_mode" value="0" />
<option name="hyperz" value="true" />