Click on the wee 'i' button lower left and this will uncover the Info Pane. You can add this kind of information to the Description Field.
There is no way of adding text on to the face of a Photo in iPhoto. To do that you'll need an external editor In order of price here are some suggestions:
Seashore (free)
Graphic Coverter ($45 approx)
Acorn ($50 approx)
Photoshop Elements ($75 approx)
There are many, many other options. Search on
MacUpdate.
You can set Photoshop (or any image editor) as an external editor in iPhoto. (Preferences -> General -> Edit Photo: Choose from the Drop Down Menu.) This way, when you double click a pic to edit in iPhoto it will open automatically in Photoshop or your Image Editor, and when you save it it's sent back to iPhoto automatically. This is the only way that edits made in another application will be displayed in iPhoto.
Regards
TD