Zhang --
My first name is Dale and my last name is Howard, but that doesn't really
matter. Since you are not using Project Server 2007 or Project Portfolio
Server 2007, that simplies things greatly. Your question, if I am not
mistaken, is how to estimate Work on tasks while the project is still in the
proposed stage. Here's how:
1. In the Gantt Chart view, right-click on the Duration column header.
2. In the shortcut menu, click the shortcut menu that appears, select the
"Insert column..." item.
3. In the Column Definition dialog, click the Field Name pick list and
choose the Work field.
4. Click the OK button.
5. Pull the split bar to the right so that you can see both the Work and
Duration column.
Now you can estimate both the estimated Work on the task, and the "window"
(Duration) during which the Work will be performed. Hope this helps.