Currently Being ModeratedSep 6, 2013 5:35 PM (in response to I\'mNeither)
Place the video in a group at the bottom of the layers list (you can do this by dragging the video layer down below everything else then over to the left edge under the checkboxes - you should see the mouse cursor change adding a green circle + and there should be a blue line with a small circle on the left end -- drop the video and there should be a new group created containing the video layer.)
Alternately, you can create a new group and place the video inside. You'll need to drag the group to the lowest level of the layers list.
Once you have the video isolated, on the right side of the group layer there's a small icon. When it's 3D it looks like 3 stacked squares. Clicking on it will toggle to 2D (and vice versa).
Once your video layer is 2D, it will fill the original video frame and you can work your 3D magic in front of it (you will not be able to move behind it!)
Currently Being ModeratedSep 7, 2013 8:55 AM (in response to fox_m)
Addtionally, if you needt to keep it as part of a 3D group with lighting, you can disable the shading from the lights. You can do this with any object in a 3D scene. Select the layer and in the properties, go to the lighting section and change the Shading setting to off.