Here you go - add it to the VBA editor and create a
rule to run a script.
Updated: fixed it so the message body is added to the task
Sub ConvertMailtoTask(Item As Outlook.MailItem)
Dim strTaskName As String
strTaskName = Item.Subject
Dim objTask As Outlook.TaskItem
Set objTask = Application.CreateItem(olTaskItem)
objTask.Subject = strTaskName
objTask.StartDate = Item.ReceivedTime
objTask.Body = Item.Body
objTask.Save
Set objTask = Nothing
End Sub