Thanks to Activision's Hellchick for passing along the following note:
We're currently doing a private beta of a Wolfenstein: Enemy Territory test. This test will have one map and we're planning on releasing it sometime in the next week. Stay tuned, we'll have more info for you as we get closer to wrapping up the private beta.
Players will NOT need Return to Castle Wolfenstein to play Enemy Territory (or the ET test we're releasing soon). ET is a free stand-alone game, so anyone who wants to play will be able to download it.
News source: PlanetWolfenstein (GameSpy)