* Go to: window > preferences > pydev > Interpreter - (Jython/Python).
* 2. Choose the interpreter you have installed in your computer (such as python.exe or jython.jar)
* 3. Select the paths that will be in your SYSTEM PYTHONPATH. It’s important to select only those folders that will not be used as the root for some project of yours.

http://www.fabioz.com/pydev/manual_101_interpreter.html