Advanced Office Key Recovery, or AOKR for short, is a program to decrypt Word and Excel 97/2000 files that have file open protection set, as well as Word and Excel XP files with default (Office 97/2000 compatible) encryption -- guaranteed, regardless the password length and complexity. This is being done by trying all possible encryption keys (instead of brute-force and dictionary attacks) and takes only about two weeks on single Pentium III/1000 PC .
More info:
hxxp://www.elcomsoft.com/aokr.html