Normally, the ESRB is a great resource for leaked information, such as the unannounced PSP version of Atari's Ghostbusters: The Videogame it rated the other day. Sometimes it's not such a great resource.
Case in point: Atari has denied that Ghostbusters: The Videogame is actually coming to the PSP and the Entertainment Software Ratings Board has since pulled the platform from its rating of the game. Atari reps tell Eurogamer that a PSP port of the ghostbustin' game is "not true."
You shouldn't be left wanting for platforms to play it on, though. It's coming to every other platform under the sun. Just not the PSP, says Atari.
Ghostbusters not coming to PSP - Atari [Eurogamer]