It's impossible to say what is happening with your DWG file contents without taking a look inside the file(s) themselves. One common error is that a file contains objects that were produced in an add-on, like the walls and other construction objects created with AutoCad Architecture (previously called Architectural Desktop). These must be converted into standard AutoCad 3D geometry in the originating application before importing them into SketchUp.
When importing, SU also ignores entities that do not form geometry, like text and dimensions, imported images and hatches.
SU version 7 cannot read the latest (2010) DWG file format.
Anssi