Photoshop :: Move And Drag From Its Layers Palette Onto Blank Background Canvas

Every once in a while I print that has two side-by-side images on one piece of paper. My usual routine is to create a new document that is larger than the two images--say, 10x8 (horizontal) with a transparent background and the same resolution as the two images that I'll be placing on the canvas (say, two 4x3's). Then I simply click on the image I want to move and drag it from its layers palette onto the blank background canvas, and move/edit/size as needed.

when I drag an image over to the blank canvas, it assumes the size of the entire canvas. so I just have the image... enlarged. With no background canvas. when I click on the new image (the one dragged to the canvas), all of the editing commands are grayed out. So I cannot resize or move it.I'm on CS5 (mac)