You do have to license the TSM server. There is a basic TSM server (almost worthless) and the enterprise server as well as another one that escapes me at the moment. The type of TSM server license you will need is based on the environment you'll be running. Some things require the enterprise license to use (DRM, Library sharing, etc) and then there is licenses above and beyond the server like DRM.
Contact your IBM reseller and they should be able to tell you exactly what you need based on the environment you're running (or will be running).
-Aaron