It isn't your place to be aNetwork Nazi for the RIAA unless you're getting reimbursed for your time and effort by the RIAA specifically for doing so. This is a distraction from your role as an IT professional.
The way I see it, you address this one of two ways. Either you have a policy that allows users to store personal information on corporate storage systems, or you do not. If you do not, you enforce it across the board. No home movies, no vacation snapshots, and no MP3s.
If you allow storage of personal files on company storage systems, you can make a disclaimer, " prohbits and will not knowingly allow you to store personal data that is illegal or could be a cause for "hostile workplace" litigation. Any personal documents of this nature that are stored on the company storage systems wil be removed, without prior notification upon discovery by Information Technology. The company is not liable for lost personal data removed from the system, in any case.
I'd go for option #1. Users should not be storing any personal data on the company network. It is a potential vector for security issues and malware, it places increased burden and expense on the company IT budget, and it exposes the company to several different kinds of liability.
But keep in mind, you're going to alienate your users and they're likely to seek methods to get around your IT regulations, the stricter you make them.