I can download the Stanford CoreNLP package but how do I install it as a functioning node in KNIME?
you don't need to download any lib or package from the Stanford NLP website. When you have the KNIME Textprocessing plugin installed you are god to go and have everything you need to use the Stanford models for POS tagging. Simply use the Stanford tagger node, select the language in the dialog and that's it. The required models are all packaged in the KNIME Textprocessing extension.