[Ken Case]

There are two ways to do this:

1. Bring up the inspector (by pressing the Inspect button on the toolbar or using the Shift-Command-I keyboard shortcut) and enter a due date in the appropriate field.
2. Add the Due Date column by selecting Columns->Due Date from the View menu. (You can also do this by right-clicking on the column headers when your view bar is visible.)

Hope this helps!