Q: How to Transfer music from e-machine to iMac

A friend has gained ownership of an iMac with Mountain Lion on it from his son and wants to transfer ALL of his music from his e-machine which is running Windows 7 with Media Player to his new iMac's iTunes.  Is there a quick and simple way to do it or does it take a disk at a time......??????  He is in Kentucky and I am in Michigan so I can not help him easily.  The help will have to be by e-mail, phone, or FaceTime.