Okay your problems could be of 2 types: drag selection or drag a layer.
By default, all new documents on CS5 are tabbed.
Scenario 1:
Suppose you have to move "Image" from Untitled - 1 document to Untitled - 2 document.
° So what you do is select the Move Tool (V), left click on the layer you want to move i.e "Image", and then drag & it to the Untitled - 2 document tab. DO NOT RELEASE MOUSE BUTTON.
° The Untitled - 2 document will now open. Just take your cursor to the workspace. The cursor changes to Mouse Cursor+Box+[+]. Release mouse button. "Image" will now have a copy of itself in Untitled - 2.
Scenario 2:
Suppose you have to move just Selection, i.e the empty space surrounded my marching ants.
Attached Images:
For better understanding, empty object with no fill or color are just Selections. If the enclose something (image, fill, color), then it's an object.
° To move a selection, using the Move Tool won't work. You will get a "Could not move the selection because the selected area is empty" error. Move Tool cannot move empty areas.
° For this, select the Rectangular Marquee Tool (M)
° When you hover over the Selection, the cursor changes to a white triangle & a small rectangular marquee box.
° Now, Left Click, hold & drag this selection over the 2nd document. DO NOT RELEASE.
° Take your cursor over to the workspace. The cursor changes to Mouse Cursor+Box+[+].
° You will now have a copy of the Selection in new document.
Is this what you were asking? Hope I was of help.
Cheers,
DMB