Ciao nathanvit,
please follow jeffa's advice and don't follow what is written in the online book linked from your home page :)

Parsing form data is not easy as it may seem and the best solution is to use CGI.pm. Its usage isn't very different from the one explained in the online book for the Mcgi module. update: keep that book, but read section 14.4, where the author describes CGI.pm.

The problem you encountered is that you are trying to read form data from $ENV{QUERY_STRING} that is filled only if you use method GET in your HTML form. When you use the POST method, data will arrive on standard input. So you have three options: change method from POST to GET or read form data from STDIN or use CGI.pm :)

Ciao, Valerio