Automatically creating a VMWare image

I want to be able to create a VMWare image, by specifying the components that should go into it, preferably in a script, and then get VMWare, or some third process, to build the machine from the specs. So I want to be able to say eg. OS - Windows 2003, Apps - Visual Studio etc, and then it builds the machine automatically from the description. I know that you can create a template from an existing machine, and use that, this is going one step higher, and building the template from a set of specifications. Any ideas?