As I recall back in AC8 the best way to import DWG was to open it by itself first in ArchiCAD. Then clean it up (civil drawings typically have a huge abundance of layers) and merge it into the working project file.
The clean up usually amounts to throwing out or hiding all the unwanted stuff and putting the rest onto a single layer. This can then be copy/pasted into the project model or saved as a module and merged/placed that way.
For referencing you can have it on the same story and lock the layer, or put it on another story shown as ghost (assuming AC8 has the ghost story feature - I can't recall for sure).
Of course placing the DWG onto a referenced worksheet is much nicer but that requires an upgrade from version 8.