if ($Intonation=="(Smiles)"):
$Intonation="<img src=Fbigrin2.gif>";
endif;
Depending on what browser you are using, the problem could be that you don't have any '"' around the image name.
Like so:
$Intonation="<img src=\"Fbigrin2.gif\">";
(not that the '"' are escaped with a '\')