If you have a nVIDIA driver you should use CUDA, and for that you should follow this link:How to Install Cuda on nVIDIA Optimus
If that's not your case and you have an ATI you should go for OpenCL.
I could make a tutorial here, how to install it, but actually in backtrack wiki you can find a very good one, done with the contribution of "g0tmi1k". Check it here: http://www.backtrack-linux.org/wiki/index.php/Install_OpenCL
I'll show you some result I got using pyrit:
Hardware:
Running in 32Gb USB drive
OS: Backtrack 5 R3
Display Card: AMD Radeon HD 6950 DirectCUII 1GB GDDR5
CPU: Core 2 Quad Q6600 2.4Ghz
RAM: 4096MB
As far as I can say, I advice the use of ATI drives to crack passwords, because they are really much faster then CUDA imo.
