Once you enter the VMD Python environment, you will find a module called ``VMD" already loaded. This module contains all the other built-in modules for writing VMD Python scripts.
VMD is not distributed with an entire Python environment. In order to use the set of libraries that normally come with a Python distribution, you must tell Python where to find the libraries. There are two primary means of doing this. The PYTHONHOME environment variable points to the location where Python is installed; the version installed at this point must match VMD's version (2.2). Thus if you have Python libraries in /usr/local/lib/python2.2, adding the line set env(PYTHONHOME) /usr/local to your startup script or .vmdrc file will do the trick.
If you have additional modules that you want to use within VMD, use the PYTHONPATH environment variable to tell Python where to find them. See any Python book for more information.
if the Tkinter module is found in the Python installation, VMD will load it at Python startup in order to make Tkinter windows work in harmony with windows created from within Tk. In addition, if you have Numeric Python installed in your system, a submodule called vmdnumpy will become available within the VMD module; see below for details.