switching from nvidia to ATI on gentoo

install binary AMD drivers

# emerge -av --quiet x11-drivers/ati-drivers

configure opengl

# eselect opengl set ati

configure make.conf

add to make.conf...

# fglrx = FireGL and Radeon for X... now called AMD Catalyst
VIDEO_CARDS="fglrx"

recompile packages effected by use flags tied to make.conf video card config

# emerge --ask --changed-use --deep @world                                                                             /usr/src/linux
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These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild   R    ] x11-base/xorg-drivers-1.14  VIDEO_CARDS="fglrx* -fbdev* -nvidia*" 

Would you like to merge these packages? [Yes/No] yes

run aticonfig to back up and write a new /etc/X11/xorg.conf

# aticonfig --initial

reboot

this all worked... tested OK