1. Sacrificing a virgin to the Data Deities.
2. Posting your computer's specifications such as OS, RAM, HD, Processor, Model, number of pizza sauce stains.
If it happens to be a .wmv file that is not opening for you, consider getting Flip4Mac and Perian. They shalt solve most of thine media viewing needs.
--J.D.
P.S. Follow Mikuro's linkypoos--VLC is another must have.