I got this from WDW News Today:
Here are the dates our “sources” have stated for the following events pertaining to the new Toy Story Mania attraction at Disney’s Hollywood Studios:
-Soft Openings begin on or around April 25, 2008
-Cast Member Previews of the attraction from April 26-27 and May 2-4, 2008
-Media Preview on May 9, 2008
-Annual Passholder Previews from May 10-12, 2008
-Media Press Event on May 16, 2008
-Official Grand Opening on May 20, 2008.