Hiding an app off the taskbar

[David O'Shaughnessy]

Hmmm I have no idea how a mailing list works, guess I'll find out soon enough ;)
What I want to know is if you can set an application to not show up on the task bar in XFce? I have an xmms system tray plugin that works nicely, but it's not so useful with xmms in both the system tray and the taskbar. I'd like to make it stay out of the task bar, even when it's not minimised. Can this be done? Thanks.