How to prevent users from downloading mp3 ?

i am a network administrator and was told by my supervisor to set the firewall in such a way that the users in my office are not able to download mp3 or video while working.
Is there any ways to do so ???

What you need is not a firewall, but a content-filter or proxy system which can stop specific types of content.

On the firewall you can block ports for bittorrent, kazaa, emule, soulseek etc.

sarhirh is right. Now depending on what firewall you currently use, the content-filtering capabilities might already be present. The port blocking can of course be readily implemented with any firewall. Could you provide details, if you haven't already solved the problem.