I found a way that works pretty well.
- You have to export your dwg to 3ds, to do this you have to download the 3DSOUT utility from http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=9481286&linkID=9240898, since they removed the 3dsout command from Autocad since release 2007, this utility works for all the later versions even though they claim only applies to the version listed there, i tried it on the AutoCAD Architecture 2009 release and it works fine. There you have on the readme file where you downloaded the utility the instructions for how to use the utility and to export to 3ds format.
- When you have already loaded the utility on AutoCAD and you are ready to export to 3ds, on the 3d Studio file Options window, you have to select AutoCAD Object type on the Derive 3d Studio Objects from options, and uncheck the Auto-smoothing option, and then then AutoCAD starts exporting to 3ds. You have to do this because its exports forms, solids and other 3d objects in different ways.
- Then you are ready to import to sketchup. Now you have a sketchup 3d drawing that works pretty well maybe you will have to applie some smoothing to some objects to get a very good appearance.