I'm having problems with this too. It works fine with Media Player under the default settings and stuff, but when using any of the WinAmp Plugins/MSN Messenger 7.0 stuff it refuses to budge.
I've tried whats directed on mess.be and Tasha's comments but neither work. Please correct me if i'm wrong, but all i have to do is check the "Show what im listening to" box, not add any of the (!Song) (!Artist) kinda stuff to the personal message?
Edit: After several MSN Messenger/Winamp restarts and several Toaster/MSN Plugin by TB reinstalls it's finally working. It seems persistance is the key here