Ordering items in Gridview

Hi All,

I have created three tables. They are: Projects, Tasks and Sub Tasks. Their Schema is as follows:

Project (ProjectID, Pname, Pdescription)
Task (TaskID, TaskName, Tdescription, ProjectID (Foreign Key) )
SubTasks (SubTaskID, Subname, Subdescription, TaskID (Foreign Key) )

In one Gridview, I need to allow the User to see a particular project and its belonging Tasks and Sub Tasks in a tree view. Within that Gridview users should be able to drag and drop to prioritise the tasks and save in database by its position. Next time, when users search that particular project he should be able to view the tasks in a way he has prioritised. For more explanation please see the below scenario:

Project A has
Task A
Task B
Task C
Task D

Users should be able to organise the tasks based on their priority and save in database. Such as:

Project A
Task D
Task C
Task A
Task B

Please advice on how to implement the above workaround in asp.net using vb.net language.