I'd like to use Startdraw to create scale drawings of AV installations so that users can clearly see what the finished project will look like.  Is that possible? 

Absolutely.
If you haven't done so already, do take a look at the movies that cover many aspects of Stardraw Design 7 at http://www.stardraw.com/products/stardrawdesign7/movies.asp
Also, you can try out the free demo, which is fully functioning and runs without restriction for 30 days.
The Rack Layout module creates 1:1 rack layouts with high detail front and rear views, and also includes a side view.
The Plan View is a general purpose CAD environment so you can create to-scale floor and ceiling plans, and general elevations.

Kind regards,
Rob Robinson
Stardraw.com