Hi all. The fix to this is... (I forget now =P).
Go into SQL (PhpMyAdmin, alike), find phpbb's database.
Open the table phpbb_music (phpbb_ being your selected prefix).
Edit each row's "code" field, replacing < with < and > with >
Man, it's been forever since I worked on this. But, it's summer break again now, and so I'll make an Admin page for it (eventually).
Note on forum hosting: I do not/will not support this until I come out with an ACP page for it.
Note on adding a link to the header: Open overall_header.tpl, and find the links section. add a link (following the format used for the other links) to music.php.