On Windows, a desktop icon is simply a "shortcut" (MS terminology for Unix "symbolic link") in your "Desktop" folder/directory. Knowing this, you can now google for "perl windows create shortcut" and find a helpful snippet here in perlmonks.
The "path" in that shortcut would be your "perl whatever.pl".
There is a "Desktop" folder for every user and a common one, which are merged on the desktop display, so that you can create shortcuts for "all users", which is what your installation script would have to do.

if your installer script can rely on having perl installed on the target machine, you were done then. Otherwise, you'd have to package your installer (and likewise your gui_simple_app.pl) as already suggested by other monks.