OK.. I'm really unable to enable 3D.
I don't know what's wrong. I can't make work the both drivers.
With my current config (x11-drivers/xf86-video-ati-6.6.1), glx is not working because it's not found :
grep -e EE -e WW /var/log/Xorg.0.log
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(WW) `fonts.dir' not found (or not valid) in "/usr/share/fonts/encodings/".
(WW) `fonts.dir' not found (or not valid) in "/usr/share/fonts/util/".
(WW) `fonts.dir' not found (or not valid) in "/usr/share/fonts/cyrillic/".
(WW) `fonts.dir' not found (or not valid) in "/usr/share/fonts/default/".
(II) Loading extension MIT-SCREEN-SAVER
(WW) Warning, couldn't open module glx
(EE) Failed to load module "glx" (module does not exist, 0)
(WW) ****INVALID IO ALLOCATION**** b: 0xf8001000 e: 0xf80010ff correcting
(EE) end of block range 0xf7ffffff < begin 0xf8000000
(WW) RADEON(0): Failed to detect secondary monitor, MergedFB/Clone mode disabled
(WW) RADEON(0): config file hsync range 30-70kHz not within DDC hsync ranges.
(WW) RADEON(0): config file vrefresh range 50-160Hz not within DDC vrefresh ranges.
(WW) RADEON(0): Direct rendering disabled
Then, I can't install the other drivers (x11-drivers/ati-drivers-8-28-8)
I first have a warning at the end of emerge.
* You don't have MTRR support enabled, the direct rendering
* will not work.
Looking into Google, I found a page telling to enable this option in the kernel :
Processor and Features --->
[*] MTRR (Memory Type Range Register) support
But I did not find a way to enable that feature in my current kernel 2.6.15 :-(. It does not seem to be there...
Then the compilation fails on :
* DRM module not built
>>> Source compiled.
>>> Test phase [not enabled]: x11-drivers/ati-drivers-8.28.8
>>> Install ati-drivers-8.28.8 into /var/tmp/portage/ati-drivers-8.28.8/image/ category x11-drivers
* Installing fglrx module
install: cannot stat `fglrx.ko': No such file or directory
!!! ERROR: x11-drivers/ati-drivers-8.28.8 failed.
So... I guess I'm really struck. I don't remember having such problems with my previous install and RADEON 9250 :-(