After Fresh installation of Ubuntu 12.10 , you have to install graphics driver to get the most of Ubuntu ,  Installing graphics Driver ( ATI AMD Radeon ) is really easy you can install graphic driver either  using .

• Software source
• Download from amd site and install it

WARNING : for old graphics card go to this page and make sure that whether your card is supported or not for unsupported cards use legacy drivers you can also verify using this page  legacy driver for unsupported cards Download

http://www2.ati.com/drivers/legacy/12-6/amd-driver-installer-12.6-legacy-x86.x86_64.zip

1 : Install using software sources

Steps

• Open Software sources

• click on additional drivers tab

• choose ati graphics from fglrx
• and click on apply updates
• enter your password and wait until it finish installing

2 : Download and Install Driver package

Download driver package : Download from here
open terminal and type

unzip amd-driver-installer-12-9-beta-x86.x86_64.zip
chmod +x amd-driver-installer-12-9-beta-x86.x86_64.run

or you can create installation package and install it using command line,
but before doing anything open Software Sources  and enable multiverse and restricted repositories click on other software and enable canonical partners

sudo apt-get install dpkg build-essential cdbs dh-make dkms execstack dh-modaliases fakeroot libqtgui4 dpkg-dev g++ g++-4.7

sudo apt-get install ia32-libs-multiarch:i386 lib32gcc1 libc6-i386
sudo apt-get install ia32-libs
sudo sh ./amd-driver-installer-12-9-beta-x86.x86_64.run --buildpkg Ubuntu/quantal
sudo dpkg -i fglrx*.deb
sudo aticonfig --initial -f
$ on xorg start failure
sudo mv /etc/X11/xorg.conf.disabled /etc/X11/xorg.conf

Done !
reboot after installation