Answer from Paris Digest, France
13:18 April 21, 2010
Paula, I checked their web site at http://www.operadeparis.fr/cns11/live/onp/site/pratique/visites/Garnier/comment_visiter/index.php?&lang=en and called them. It is not possible to book in advance. There are visits on Wenesday, Saturday and Sunday at 11.30am and 3.30pm. Just go there and buy a ticket at the Opera. Enjoy your stay in Paris.