CUDA is freely available. If you have a machine with an NVIDIA GPU (including a laptop), visit NVIDIA’s Developer Zone, where you may download CUDA and get started. Here are Fred Lionetti’s notes (somewhat outdated), on how to install CUDA under MacOS or Ubuntu. The definitive source of information and software is the Developer Zone site, where you will also find a good deal of Documentation. The web site provides (free) downloads for the drivers, toolkit, and SDK, together with downloadable applications.
Be sure to use the documentation for port you have installed (e.g. MacOSX, Linux). See http://developer.nvidia.com/object/cuda_3_2_toolkit_rc.html to obtain documentation for CUDA v. 3.2.
Of note:
Here is a web page of GPU Resources
Maintained by [Thu Feb 24 23:55:31 PST 2011]