I've been trying to figure out how to use cron to schedule reminders that provide an alert in a GUI window even if the Terminal isn't being used. The problem is that osascript can't be used if user feedback is needed. Display dialog won't work with osascript, but you can use osascript to tell the Finder (or some other application) to do something, which can include "display dialog." Then, the Finder apparently handlies the Apple Events that osascript can't from the command line.
Try adding these commands to your crontab file (see earlier hints for help on cron.
Use dialog:
osascript -l AppleScript -e 'tell Application "Finder" to display dialog "Call Frank" '
Speak text:
osascript -l AppleScript -e 'tell Application "Finder" to say "Call Frank" '
Use alert:
osascript -l AppleScript -e 'tell Application "Finder" to display alert "Call Frank" '
Now, if I could just figure out how to do this with a floating, modeless dialog and have it catch cron events that took place while the computer was off or sleeping....
Mac OS X Hints
http://hints.macworld.com/article.php?story=20021029062059486