Event2ToDo

Event2ToDo lets you schedule the creation of To Do items in iCal. This is useful when you want to enter a task into iCal but you don't yet want it to appear with all the others in your To Do list because you can't start working on the task yet.

Simply create an event for the start date with any due date in the comment, attach to it this AppleScript as an Open File alarm, and the event will automatically be converted into a todo item at your chosen time.