I will talk in Autocad terms here.
If you want to import a cad drawing without solids, you will have to prepare it for export to blender.
First you have to scale the drawing to have a size total of -15,-15,-15 to +15,+15,+15 . otherwise blender can import it... but you won't be able to "fully see it" in blender.
Now the tricky part:
- If your drawing "don't have solids" (regions, solids, bodies, don't confuse them with "3d meshes" with aren't solid in AutoCAD) you can export the CAD Drawing to DXF (if you're using Autocad 2004 or latter, you can just save as DXF format, using the "saveas" command, older versions have to use the "dxfout" command), and import it to blender.
- But if your drawing contain solids, blender can't recognize them (The solids data in autocad are propietary, and is encrypted to prevent use from other software without the neccesary licence code), so you have to export it in 3ds format. (using the "3dsout" command). Note that you have to get the import script for 3ds and copy in the /.blender/scripts folder before you can use it) (scripts are in this page: http://bane.servebeer.com/programming/blender/#3DS
Note for the last option that if the drawing contains many Solids you will have to asign a unique layer/color for each solid to be able to edit them in blender. And note also that in the conversion process some data will be lost and/or results may vary from the original drawing in cad. That's product of the conversion to 3ds made in autocad.