I use a Mac OS Lion. When I drag an image onto my page in Photoshop it shows up tiny and I have to increase the size. It isn't like this on my other devices. Can you please tele where or what the setting is to make this show up as an actual size?
Check the resolution and physical size specifications of the image you are dragging into, and the image you are placing.
Most likely the resolutions are very different, and the physical size of the placed is being honored, which would make it smaller (or larger) in the parent document so that the physical size is correct.