Sng;
Are you _sure_ you want to xref dwgs into Archicad. There may very well be 'better' ways to achieve that which you want to do.
However to answer your question, no, archicad doesn't convert lines into chairs, columns, walls etc. automatically. Understandable, I think.
However there is an Archicad add-on (for sale separately) called Plan2Model which will facilitate repetitive 'raising' of a (scanned or otherwise) 2d drawing. Generally considered useful for archiving etc. purposes, not for 'one off' projects. The equivalent (similar) Autodesk compatable product is scan2cad.
"What else should I know about line vs. object" - this is about the whole genus of 3d/modelling programs vs. flatland (drawing) programs. There is a big difference between a 'dumb' line and (more or less) 'intelligent' objects. There are probably threads on this over at the revit forum too...
- Stuart