I am trying to move all of the tasks in a project along by two weeks, i have tried changing the project start date, but the tasks stay at the same date.
This is one of the reasons that everything that you enter should be linked. Without links, you'll need to do them one at a time.
It's possible that there might be a macro that you could put together a macro to do that. You could try the macro recorder to see what code looks like and modify to do the remaining tasks