When I first started experimenting with Render this used to bug me too. I have the fix for it. At the command line type in ARX <enter> and then Unload <enter> acrender(for R14 and R13 enterRender in place of acrender)<enter>the render window will be unloaded.
Good luck! Jim
Jim,
I was trying out Rendering the other day and I noticed that the Render window would not go away. I tried closing the window and it wouldn't close. Is there any way of getting rid of this pesky window without exiting AutoCAD?