I know this is less programming related and more time management related, but I value the feedback of the users on this site. I\'m finding myself particularly busy this semester
I highly recommend Request Tracker, as did J.J. It can be hosted yourself, and I believe it runs on Windows. (Since it runs on UNIX, it should run on Mac OS.) I don't know of any Gantt chart functionality for it, but I'll bet there are reports for it that could do that.
I'm just answering to plug Request Tracker, not for the bounty. If for some reason you decide to go with RT, make sure you give J.J. the bounty, as he recommended it first!