First, congrats on getting to present to such a large audience, your work must be very respected. More to your point, I have two ways I typically go about it.
If you want the users to see EXACTLY what they will be using, I go with a published version on Tableau Server. It will show them exactly what kind of processing time they will be dealing with, how it will look, and what interactions (if any) there will be. However, this obviously runs the risk of complications due to other issues.
On the safer side, you could take screenshots of your dashboards and display them using any other means, PDF slideshows, PowerPoint, or any other software you may use. However, this lacks the interactivity.
In my experience, I show the pictures to them as an unveiling. Then, we invite them to be a part of the pilot group, in which they can use the live version in whatever way they want. It allows them to fully experience the product while also giving you valuable feedback from a real business user.
Hope this helps,