I never used perlscript before, but as I'm seeing it, you're never suppling a value for your textfield. That way, the contents of that textfield will always be empty. Try this:

Code:
<HTML>
<HEAD>
<META HTTP-EQUIV="CACHE-CONTROL" CONTENT="NO-CACHE">
<TITLE>formtest</TITLE>
</HEAD>
<BODY>
<FORM NAME="myform" METHOD="GET">
<INPUT TYPE="text" NAME="mytest" VALUE="Foo">
<INPUT TYPE="submit">
</FORM>
<SCRIPT LANGUAGE="PerlScript">
$mytest = $window->document->myform->mytest->{'Value'};

$window->document->write("Debug: $mytest\n");

</SCRIPT>
</BODY>
</HTML>
I can't test it, since I have no activeperl installed. You should get something in your textbox, and that same word should be printed in the body of your page, as far as I see.

By the way: you should also specify that your form uses the GET method to send those variables (<FORM NAME="yadda" METHOD="GET"&gt.