The My Neighbor Totoro DVD cannot be purchased currently. However, by submitting your e-mail address to Amazon, they can report the number of interested buyers. Effectively, this is a petition on Amazon.com for the release of My Neighbor Totoro.
The Princess Mononoke DVD is also available. This title may be pre-ordered. The release date is scheduled to be January 1st, 2001.
On the Technical Information page for Mononoke, it only lists the English dub. But, confusingly enough, the Mononoke Castlist page lists both the Japanese and English voice actors.
Please consider the state of the Mononoke DVD "unofficial" until Disney announces otherwise.