Why can't I publish only new assignments?
The publishing process in Microsoft Office Project Professional 2007 has been modified so that all fields are published at once and all assignments are sent to all resources. As a result, you can no longer publish only the new assignments in your project.
Note Once a task has been published, only changed fields will be republished. If you don't change any data on a task, the publish process will not resend the task data to Microsoft Office Project Server 2007.