Email:
The ISO/IEC 9796:1991 standard has since been withdrawn,
but can still be purchased.
A free online source is section 11.3.5 in the excellent Handbook of Applied Cryptography.
I announced the attack on August 30, 1999 in an sci.crypt.research post.
Here is the mentioned file with messages allowing the attack. Same gzipped, for hash verification purposes.
This page was revised on 2008-03-01