This is part one of the St. John Passion, provided to assist priests, deacons, cantors and choirs to learn how to sing the Passion on Good Friday. It also happens to be one of the most sublime recordings of chant ever made - the cadences when the narrator introduces the words of Christ are particularly well sung. I urge you to buy one of the Naxos CDs which has this chant on it: In Passione et Morte Domini: Gregorian Chant for Good Friday or Ultimate Chant.
Here is the pdf of the music.
There are very good English arrangements to be found.
Update
Video of one such English version from St Mary's Cathedral on 29 March 2013 (with the crowd's parts being sung to an arrangement of T. L. de Victoria):
And another version, Latin, with the original Victoria setting for the crowd:
Also for Good Friday - the Improperia. This is Victoria's setting, sung by the Choir of Men & Boys of St Thomas Church Fifth Avenue, New York under the direction of John Scott. Recorded live on Good Friday 2011.
