Adding debian experimental repo is not a good idea. If you want to build the fglrx legacy driver for ubuntu:

Code:
cd ~/
wget http://www2.ati.com/drivers/legacy/amd-driver-installer-catalyst-13.1-legacy-linux-x86.x86_64.zip
sudo apt-get install build-essential cdbs dh-make dkms execstack dh-modaliases linux-headers-generic
unzip amd-driver-installer-catalyst-13.1-legacy-linux-x86.x86_64.zip
chmod +x amd-driver-installer-catalyst-13.1-legacy-linux-x86.x86_64.run
sudo sh ./amd-driver-installer-catalyst-13.1-legacy-linux-x86.x86_64.run --buildpkg Ubuntu/precise
sudo dpkg -i fglrx*.deb
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.bak
sudo amdconfig --initial -f
If it still doesn't work well after reboot, then maybe you should try a different desktop environment (like lxde).