Nenners is a volume rendering tool, however it is specifically designed for medical datasets. It is available for Apple OS X, Linux/UNIX, and IRIX, for both 32 and 64 bit systems.

Download:
OSX: 32-bit, 64-bit
Linux/UNIX and IRIX: source

Install:
OS X Easy, just put the drag and drop the package in your applications folder.

UNIX style systems: Unzip the tar ball into your desired destination, then run make.

Windows: Go get an Apple and follow directions above. Or if that just isn't possible install a free version of linux (suse is my favorite) and follow directions above.

Test:
After installing download - this - dataset. Next download - this - transfer function. Then download - this - parameter file. Finally type "nenners @params.txt".