The letters (a kind of poem) are from "Makurano sousi" which was written in 990s by Sei Shonagon. The English version was published as "The Pillow Book of Sei Shonagon" in 1928 by Arthur David Waley.
The meaning of the letters is:

"On a bright moon light night
Crossing a river on a coach led by a bull
How tasteful it is to see scattered water,
made by bull's each step, shining like breaking crystal."

-Translated by Taku Nagai with a little help from Naojiro Minami-

The hand writing of the poem was done by Madoka Hasegawa at Tohoku University

Poster created by the 2007 Local Organizing Committee from Kyoto.