Headless MacMini

Do you have another computer and a home network?

Screen sharing works very well for me!

Are you logging in to the Mac Mini from another PC? If so, the terminal command "shutdown -h now" for halt or "shutdown -r now" for reboot. These are standard Unix commands.

If you have another Mac (10.5 or above) or an iPad or iPhone, you can remote into the Mini and control it as if you were sitting in front of it. There are two steps to get this working. The first step is to configure the Mini to allow screen sharing. Here are instructions if your Mini runs 10.6 (Snow Leopard):

Mac OS X 10.6 Help: Sharing your screen with other computer users

Instructions are similar if your Mini runs 10.7 (Lion):

OS X Lion: Share your screen with other computer users

The second step is controlling the Mini from another Mac:

Mac OS X 10.6 Help: Sharing the screen of another computer

OS X Lion: Share the screen of another computer

If you don't have another Mac, iPad or iPhone (heaven forbid), but you have a Windows computer, you can use VNC software. You still need to configure screen sharing on the Mini (first step above). Then, you need to get the VNC software on your Windows computer and configure it. Here are some good options:

http://www.wyse.com/products/software/mobility/PocketCloud
http://www.tightvnc.com
http://www.realvnc.com

I hope this helps!

This might be the simplest solution for shut down, but it requires a keyboard. If you press these four keys at the same time (Control-Option-Command-Eject), it will quit all apps and shut down the computer without any more interaction on your part. If you have any unsaved files open (unlikely if you're only using this as a music server), it will give you a chance to save changes.

I do control my mac mini with either an ipod touch or iphone and will try the screen sharing recommendation.
When I first got the mac I tried the VNC route but never got it to work as I'm not the most computer savvy guy. Maybe I'll get my 14-year-old grandson to set it up. ;)