This beta release is for developers on version 10.5.2 Mac OS X on Intel-based MacBook Pro with 256MB GeForce 8600M GT (128MB MacBook Pro may work, but this is not a recommended configuration for CUDA). And Intel-based Mac Pro with either Quadro FX5600 or GeForce 8800 GT. These cards need to have the Apple EFI.
Install the Software Update to 10.5.2 and after the reboot, go through Software Update again to get the Leopard Graphics Update.
Then install the CUDA Toolkit and SDK for Mac OS from http://www.nvidia.com/cuda