vbox.launchd.plist

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" 
        "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> 
     <plist version="1.0">
      <dict> 
        <key>Label</key>
        <string>myvmname.virtualbox</string>
        <key>ProgramArguments</key>
        <array>
          <string>/usr/bin/VBoxHeadless</string>
          <string>-v</string>
          <string>off</string>
          <string>-s</string>
          <string>MyVirtualMachine</string>
        </array>
       <key>RunAtLoad</key>
       <true/>
       <key>ServiceDescription</key>
       <string>Virtual Box VM Launcher</string>
       <key>UserName</key>
       <string>[YOUR USERNAME HERE]</string>
      </dict>
    </plist>