Iphoto

Is it possible to insert a text e.g in the bottom of a picture in Iphoto ??: If yes, how to do D

You can do that in preview or with 3rd party apps like skitch

As Poolman says above, you can't do it in iPhoto. You can make a copy of the photo by dragging it to, for example, Preview (or as mentions Skitch, and there are other options as well) and adding text.

Apple's prosumer photo application, Aperture ($80) allows basic watermarking if that's what you're primarily interested in doing (and with the Border FX plug-in can do more elaborate watermarking).