how do you upload seperate parts of your assembly into grabcad?

use pack and go feature
http://grabcad.com/questions/tutorial-pack-go-feature-in-solidworks

When I put an assembly onto grabcad, I first make a zip. folder on my desktop and place all of the part and assembly files I want/need to include into that folder, then that zip file is the one i upload.

Sudhir Gill's solution is a bit more elegant then mine and I cant wait to try it next time, however, if your part is not too complex and you want to include additional files such as a rendering or drawings my solution does the same thing without having SolidWorks do it for you.