I was wondering if it would be possible to direct the sound from Spotify to speakers, while keeping Skype or Google chat to my headset? I am using a mac mini by the way
It has detailed instructions on how to select audio devices for Skype. In general, most applications (especially VoIP software) will have the option to select devices manually and to override system audio default.
EDIT: Seems this has been asked before in a similar fashion:
is what you want, see also: