WELL, I THOUGHT IT WAS SOLVED COZ I HAD DIRECT RENDERING BUT NOW MY SYSTEM
HANGS CONSTANTLY!!!

I followed  this Howto step by step, I've tried to do it with modules or
with built-in mode but my Gentoo continues hanging, for example, when I run
glxgears and tvtime both together. I don't understand it!

So here you have some relevant info (ask for more if necessary please!!) :

gentoo ibai # lsmod | grep 'drm\|agp\|rad'
radeon                107040  1
drm                    64148  2 radeon
radeonfb               85824  0
fb                     42920  1 radeonfb
i2c_algo_bit            9096  2 bttv,radeonfb
cfbcopyarea             3840  1 radeonfb
cfbimgblt               3072  1 radeonfb
cfbfillrect             3712  1 radeonfb
i2c_core               16912  6
tuner,bttv,tveeprom,radeonfb,i2c_algo_bit,i2c_i801
intel_agp              19996  1
agpgart                28872  2 drm,intel_agp

gentoo ibai # zcat /proc/config.gz | grep MTRR
zcat: /proc/config.gz: No such file or directory

gentoo ibai # lspci | grep -i radeon
01:00.0 VGA compatible controller: ATI Technologies Inc Radeon RV100 QY
[Radeon 7000/VE]

I attach my .config: