DXF is ok, Qcad also read DXF files. (Im using it already)
So we can say, that THERE IS NO GPL CAD SOFWARE, THAT READS DWG FILES. (november 2006)
The next thing to do, to get working with DWG, is to convert it from DWG to DXF.
and I found it's possible.
1. Im converting with LX-viewer DWG to DXF.
2. Then open DXF with Qcad.
probably there are better solutions, but I don't know them.
Good topic anyway.