Ghibli Museum, 1-1-83 Shimorenjaku, Mitaka, Tokyo JAPAN, http://www.ghibli-museum.jp (Japanese), http://www.ghibli-museum.jp/ticket/overseas.html (English)
JTB USA Ghibli page. (Sells ticket vouchers to non-residents of Japan.) http://www.jtbusa.com/enhome/gbl.asp
Lorenzo Conti's fan site. http://digilander.libero.it/joe.chip/ghibli_e.htm (This site's information helped me out so much.)
The Ghibli Museum: A Survival Guide, Jan. 2004. http://anime-tourist.com/article.php?sid=607 (I walked over to the museum [15 to 30 minutes] from the train station, but this article tells you how to take the bus.)
From "My Travelogue Manga of Japan (Sans Drawings)," by K. Avila, Sequential Tart, May 2006, 29 March 2006 entry:
... Instead of returning to Shinjuku, I end up by mistake going to Mitaka in the opposite direction. I decide to go to the Ghibli Museum since I'm in the area. Surprisingly, the Mitaka JTB office still has tickets* (sold only to foreign tourists with a passport in hand). The Ghibli Museum is best enjoyed from a child's perspective, since it's geared toward them, which is why I left it off my original itinerary (well, I had also been there before).

*I was very lucky. It is highly recommended you have your ticket or ticket voucher BEFORE you go. The first time I went, when I was living in Japan, I think I waited a month-and-a-half to get a weekend ticket. The photos below were taken during my March-April 2006 trip to Japan. Photography is not allowed indoors.
Totoro
The Totoro Entrance		 entrance
entrance		 entrance
entrance		 back side
view from rear right side of entrance
patio area
patio area with gazebo		 Straw Hat Cafe
Straw Hat Café		 Straw Hat Cafe
Straw Hat Café		 Straw Hat Cafe
Straw Hat Café
garden roof robot
garden roof with robot from
Hayao Miyazaki's Castle in the Sky		 garden roof robot
garden roof robot		 garden roof robot
garden roof robot