Well it's easy enough to have iCal send out an e-mail reminder to you before an event. However, it does not seem like you can specify the e-mail address, the pull down box only contains one address. The address is taken from your address book; it's the address card that you have set to be "mine" Card -> This Is My Card.
If you want to hack and change the e-mail address for say just one event, then you could drop into terminal and type cd ~/Library/Calendars and edit the calendar. Find the event (using the SUMMARY field), and then edit the line:
ATTENDEE: mailto:Change the e-mail address to what ever you want. Make sure that iCal is not running when you do this!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20021018060343300