Follow this page to get the Current Drivers from non-free repo installed:
https://top-hat-sec.com/forum/index.php?topic=3160.0

Download the script here: https://docs.google.com/file/d/0B3s5DO68wWL-cXBrOGlCUHRCTFU/edit?usp=sharing&pli=1

Then, install the AMD-APP-SDK.

Download from here: http://developer.amd.com/amd-license-agreement/?f=AMD-APP-SDK-v2.7-lnx64.tar

Must be version 2.7 , as it is the one compatible with the 12.6 non-free repo Radeon Driver

Then, these packages must be installed, to get cmake and cmake++

apt-get install libboost-python-dev zlib1g-dev libssl-dev cmake libboost1.49-all-dev

Before we can install cmake++ we need to set the ATI Stream paths:

echo "ATISTREAMSDKROOT=/opt/AMDAPP
export ATISTREAMSDKROOT" >> ~/.bashrc
source ~/.bashrc

Now we can proceed with the installation:

svn co https://svn.code.sf.net/p/calpp/code/ calpp
cd calpp/trunk
cmake .
make
make install

Install additional package to be able to compile Pyrit

 apt-get install libpcap0.8-dev

In addition now we can install Pyrit with the OpenCL option.

svn checkout http://pyrit.googlecode.com/svn/trunk/ /tmp/pyrit
cd /tmp/pyrit/pyrit && python setup.py build && python setup.py install
cd /tmp/pyrit/cpyrit_opencl && python setup.py build && python setup.py install

Now we can test Pyrit.

pyrit list_cores
pyrit benchmark

Article References:
http://www.backtrack-linux.org/wiki/index.php/Install_OpenCL which is for BackTrack.