If you're looking at your Google Calendar in the full month view, and you click on a day to create an Event, you'll see a new option to create a Task...

The Due Date for the Task is automatically set for the day you clicked on.

http://img177.imageshack.us/img177/4664/createtaskoption.gif

I'm reasonably sure that's been there since Tasks was integrated with Google Calender.

and I can confirm what Tony said.

You're right, thanks guys.
http://gmailblog.blogspot.com/2009/05/tasks-now-in-calendar-too.html