I can’t say I’ve ever seen Blender Render bake to a random texture. So long as you select all UV’s in the UV/Image editor and then select the image you want to bake – effectively assigning the image to the mesh’s UVs – the bake should go straight to that selected image.
Double check that you don’t have “Cycles” enabled when you bake. The selection/assignment setup is different over there.
If the problem persists, upload your .blend file to dropbox (or similar service) and post a link to download here. I’ll take a closer look.
