Ever since the last upgrade to version 8, SketchUp no longer offers the possibility to import DWG files to the free version of the software. Only the Pro users can use a native solution to directly import DWG files to SketchUp. Are there any workarounds? Sure! I was browsing some articles about SketchUp last week when I found a great way to still use DWG files with SketchUp 8. The solution? Keep both SketchUp 8 and 7 installed on your computer.
With the free version of SketchUp 7, we can import DWG files using a plugin developed by Google itself. Today, we still can download SketchUp 7 at this link, even with the label saying it is the Pro version, after 8 hours it will turn automatically into the free version.
Just be careful not to mess up your SketchUp 8 install folder, if you decide to install SketchUp 7 with version 8 already installed.
Source: JIM'S SKETCHUP [PLUGINS] BLOG
Should I uninstall SU8Free and then install 7 and then reinstall 8Free to be able to import DWG files?