There are a few things to do that will help you import autocad drawings into SB
1) Check your units in both autocad and also SB, if Sb thinks that your units are in miles and not in inches, you probably won't be able to see it. It is probably best to set the units in both programs to inches/feet.
2) Make sure that at least part of your drawing in autocad is located at 0,0. This is center of what gets imported.
3) When importing to SB, there is a setting in the view menu called outline/wireframe. If you click this, the black background will disappear and you will be left with the objects you created in autocad.
When importing autocad drawings into Corel 12, the first two of the above suggestions apply and you will be asked to choose the file to import. After you do a window will pop up giving choices as far as 3d projection and scaling. If the drawing you are importing is coming in as a single line instead of the shapes you drew in autocad, then there may be a problem with the 3D projection. If you created the drawing in top view, you want to make sure that is what is showing in the 3d projection. If you created it in top view but it is showing front view in the 3d projection then the program will just see that view of your drawing and it will show as a single line.
I was able to import autocad R12 and R14 into both SB and Corel. If you have an earlier version you can get a free download of a program called dwg gateway. It will convert one version into another. Here is the link: http://www.dwggateway.com/.