My objective is to have the record spinning in the crater, so I need to merge the two projects. What's the best way, if any, to accomplish this?
Use a consistent set of materials for a Render engine. Cycles Render or Blender Render. Do not mix Cycles and Blender materials.
It appears you have tried to mix materials for the two different render engines.
If you are producing a single still photo you may be able to render one image as transparent .png file. You may be able to render the album disc as a texture and apply it as .png which is render engine neutral.
I agree with atomicbezierslinger that your problem is that you tried to combine two different material protocols, the Blender Internal render for the landscape, and the Cycles render for the vinyl disk. But if you want to merge the two, what I'd do is to take an image of the disk by placing the a camera perpendicular to the plane of the disk, and take a screenshot, saving it in a suitable format (e.g., uncompressed, single-layer tga). Then I would take that image, and use the image to place an image texture on the disk you imported into your Blender Internal project.