Indeed you may create slides "from scratch" in Captivate. You
are correct in that there are no drawing tools. About the closest
you can come with those is to use Highlight Box objects and adjust
the Frame Width. Lines are another story.
The bottom line is that Captivate doesn't function quite like
Flash in that you create illustrations. It is more of a screen
recording application. Grabbing screen captures and stitching those
together with mouse movement and bits of full motion to achieve the
illusion of a full motion product.
Not sure what to advise regarding the line in change.
Personally, I've never used it. Hence, I've not seen what you are
describing. Perhaps another user can speak to that.