A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
As I recall, this came up once before and we concluded that there's no way to make PPT do this, short of writing and installing an add-in.
But
Go to Office Button | PowerPoint Options | Advanced
Under Display, remove the check next to "Show all windows in the task bar"
Click OK
Now there will be a small black X beneath the bigger red X in the upper right corner of the PPT window.
Click the smaller x when your new blank presentation opens automatically; that'll close the presentation w/o closing PowerPoint altogether.
Or just leave the blank presentation open. Normally it's not going to hurt anything or eat enough resources to be worth worrying about.