There’s currently a discussion going on in the forum about how to set your current playing song in build 604 of MSN Messenger 7. The author of the Toaster plug-in for Winamp, shaneh, posted the C source code for it and silverspeed has posted working Visual Basic 6 source code.
CookieRevised has also written a lot of improved code with detailed commenting.
Update: Newer releases of MSN Messenger now use a different method, shaneh already has it covered. Check out both topics for full information.
thanks