Am I able to bring an AutoCAD 3D solid DWG into Inventor and make modifications and if so what is the easiest way?

Are you using the latest version of Inventor? If not, you will need to save your Autocad 2010 drawing down to a version that your copy of Inventor can read. From there, you should be able to Import your CAD file.You might want to take a look at this: http://lynn.blogs.com/Booklets/3134136_making_the_leap.pdf