http://bimmanager.blogspot.com/2007/10/revit-grids-in-navisworks.html
Since then I've found those grids to be fairly ineffective, it takes way too much time trying to select the grid to get into the properties.
So I created a similar family but it has a grid marker arrayed so the grid location shows up all along the grid. This has made working in Navisworks a million times easier.
Setting it up in Revit has not changed, so follow the instructions from the original post.
It can be downloaded here