Jeff:

Thanks for writing. You will want to install the free updates at www.steinberg.net. There, you will find updates that are continually improving the MAC and PC versions. I have 4.1.2.851 running on my MAC Book Pro and it barely touches the CPU. Runs smoothly.

Cubase 4.1.2.851 Update Mac OS X [Feb 4th, 2008]
Officially compatible with Mac OS X Leopard (version 10.5)
Requires an already installed Cubase 4 version on your computer!
It is recommended to install the latest Syncrosoft License Control Center after finishing the update installation.