In iCal, when you set an alarm for an event, you can tell iCal to send you an email reminder when the alarm goes off. But you can’t send notifications to email addresses that aren’t yours, for some reason beknownst only to Apple.
A workaround is to add other people’s email addresses to your entry in Address Book, with a custom label set to their name. Now that label and email address will show up in the iCal email alarm drop-down box, and you can remind other people of things, instead of just yourself.
[robg adds: This works really well; just open Address Book, edit your card, and add a new entry in the email address section. Click on the automatically-chosen label (“work” or “home,” for instance), and select “Custom…” from the pop-up menu. Enter the desired recipient’s name, and then put their email address into the email side of the entry. When you return to iCal, you can now choose this name/email address in the alarm menu’s email pop-up. Very nice — hopefully Apple will eventually allow this behavior without the hoop jumping…]