There are services available that can crack the password. Unfortunately, they are not free. Just search the net for password, password cracking, ... to find such services. Many of them do focus on Office products, so finding one should be easy.
I actually wrote an application to do this, but it takes a long time to run because it tries all alpha-numeric combinations (brute force method). It works fine if the password is 3-4 characters long, otherwise it could take weeks to find the password. If you think that the password is short, I can send you the code. Just let me know.