Go this route:
- System Preferences
- Choose "Screen Sharing" and check the box to turn it on
- Click "Computer Settings..."
- Enable the "VNC views may control screen with password:" option and give it a password. Password length is limited to 8 characters.
Now you can connect to and control your Mac from your favorite VNC application, including free versions like Mocha VNC (Lite) for iPhone or Chicken of the VNC for Mac. I personally use Mocha VNC and it is a very good VNC app for my casual use. It is surprisingly fast over my home network Wireless-G iPhone 3GS to Gigabit-connected early-2007 iMac, and it works perfect with my iMac's dual monitor setup. It's the best Spotify "remote" I've found yet.