All I do is drag and drop it into whatever project I want it in. I use a Mac so I just open aperture and mail and and have them side by side sharing the screen and click on the image (or image icon) and drag it over to the project I want it in. As you drag it and hover over the project name your pointer will show a green + sign so all you do is release it there. If you simply drag it over to the inspector pane under your list of projects and drop it there, it will open a new UNTITLED PROJECT which you can then rename. I suspect there are many other ways, probably some much easier, but that is pretty simple.