Running a command on startup

[box]

I've been trying to get the 'Stolen MacBook tracking script' here working on my MBP, but seem to be having some trouble. The actual script works fine, but I can't seem to get the system to launch the .plist file at startup. I've confirmed it isn't running with a 'sudo launchctl list' command. However, I can successfully start it manually using 'sudo launchctl load -F /Library/LaunchDaemons/checkin.plist'. I don't know my way around terminal that well. These are just commands I've picked up from scouring discussion forums!

The plist file reads as follows:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" 
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>

	<key>Disabled</key>
	<false/>

	<key>Label</key>
	<string>checkin</string>

	<key>Program</key>
	<string>/Applications/Utilities/checkin</string>

	<key>ProgramArguments</key>
	<array>
		<string>/Applications/Utilities/checkin</string>
	</array>
	
	<key>StartInterval</key>
	<integer>1800</integer><!-- run every 1800 seconds -->
	
	<key>RunAtLoad</key>
	<true/>

</dict>
</plist>

I'm at a loss. Can anyone shed some light?

Cheers!