Yes, the Vegas production will be 90 minutes and the most amazing version you'll ever see of the show (as far as spectacle goes- there will be a real lake on the stage!)...and there will be three shows a day..there will be more than one cast.
Hal Prince is going back and redirecting the entire production, he's very excited about this chance to update the show. It should be worth a trip to Sin City to check it out.
Yes it will be opening at the Venetian in Fall of '06 (as of now), but anything can change. They are building a gondala/waterway inside the actual theatre. I drive by almost daily, and it seems to me that they are already begining construction on the theatre. Venetian will also be the future home to the BLUE MAN GROUP around the same time as HAIRSPRAYs arrival.