Automate sending an email / SMS at computer shutdown

I have a client that wants to have an email message or SMS message delivered to his cell phone when his Windows XP computer shuts down due to a power failure. I have part of the solution as an interruptible power supply that has software that will allow the system to be put into hibernation when power goes out. Now all I need is a program that will sense this shutdown and email/SMS the client before it starts the shutdown procedure. Any ideas? Any free/shareware programs?