Only one onscreen window in Win version of PT?

Hi,

I'm just learning the SCREEN command, and so far have written a small
program that simply displays a black screen, and then uses ASK to
present a message "Click the mouse to continue" in the font and size
of my choice. This works fine.

However, if I try to add another SCREEN command to open a rectangle of
a different color, I get an error saying that only one onscreen window
is allowed in the Win version of PT.

Here's my question; I'm trying to design a visual search experiment,
where the subject will have to pick a target letter among a set of
distracter letters displayed simultaneously on the screen.
Theoretically, this will require me to display as many rectangles as I
have stimulus elements that must be searched. If I can only open one
window at a time, how in the world am I going to be able to display
multiple objects in one window?

Should I try and open them all in offscreen windows, composite them
into a single window using the COPYWINDOW command, and then copy that
resulting window into the onscreen window?