Update: In AC10, you can place a DWG in the floor plan as a drawing. Place it on the story below, show that story as a ghost, and trace away.
While leaving behind what you don't want. You and your project will be a lot happier if you merge only the elements and attributes that are needed.
I assume you've already opened the DWG.
1. Isolate the desired elements. Hide the layers of the stuff you don't want. Right-click on an unwanted element, select Layers, then Hide Layer. You can select more than one element at a time.
2. Move the good stuff to the Archicad layer. Once you have only desired elements displayed, select everything, then Edit Selection Set (Cmd+Opt+T).
2.1. (Hygenic, but not critical) Where applicable, change the linetypes of the solid lines to 'Solid Line'. Keep dashed and other custom linetypes as is. Change the linetypes of these when you get back to the project file.
3. Save a Module. With everything still selected, Copy (Cmd+C). Save As. For the format, choose 'Module from Clipboard'. Save the Module in a sensible place in the project folder. I recommend usually keeping it in the same spot as all the other files associated with the DWG, with the same name.
4. Merge the Module. Open your project file and go to the appropriate window and view. Merge (Opt+M). Paste to original location, Zoom to pasted elements.
For some reason, ACAD people often draw thousands of feet from the global origin. A tip: Before you drop the merge, drag it by clicking on a detectable point, then do Previous Zoom (Cmd+[). This gets you back in your neighborhood. Then drop it where you want.
5. Change the layers. Don't leave elements on the Archicad layer, in general. If working in a S/E, move the elements to +A Misc Line. If in plan, you know.
6. Change the linetypes. Switch weird merged linetypes to regular ones. The weird names are typically all caps and have names like BNDRY-EX-ISO-23BGHWQ. Once you've changed them all, use Attribute Manager to delete the weird ones.