Dragging one image into another was an easy process in almost every version of Photoshop until Adobe had a "better" idea in CS4. In CS4, they started opening each image, by default, into its own overlapping tab. That meant that unless you rearranged the default tabs, you could only see one window at a time. I find the process of dragging one image into another to be quite clunky in tabs and harder to make work. In this video, I'll show you how you can can drag and drop in the tabbed interface and then show you how to make the tabbed interface go away. I have never found a circumstance (other than a demonstration like this) where I needed to go back to tabs. However, take a look and try it both ways. Neither one is wrong or right; in Photoshop, you have the choice of how to work. Click the play button to see it in action.
--Sherry aka the prancingpixel