Hi,
Did you paste the whole script? It lacks lots of statements to be considered valid (for example it doesn't create a new virtual drive, no idea where the installation goes, probably in the default virtual drive).
Messages do not support localization (eval_gettext support).
Because of the (usually useless) start /unix the installation starts asynchronously, so I guess the installation wizard window closes before the installation is completed.
The script is not creating a shortcut to the newly installed program either.
Have you read the documentation ?
("Scriptwriter's documentation",
http://www.playonlinux.com/en/documentation.html)