More properly called The Tschai series, it's widely known as The Planet of Adventure Series of which there are 4 books.
It's the combination of SF and fantasy called Planetary Romance. His stuff is a little grimmer than the older type, though.
It's from his own book store and will apparently be available for free for a few days
http://www.jackvance.com/ebooks/shop...view&q22_id=22