As these fields are already hidden fields in your current form, all you need to do is to set them to the values you want and then submit that form. What is your code? Most likely $ie->form->submit should Just Work.

Here is my code I'm testing with, but it complains that fields_ref is unknown and using fields results in another error. I'm lost...

use warnings;
use strict;

use WWW::Mechanize;
my $mech = WWW::Mechanize->new();

my $id = '14632';

my $url = "http://home.myspace.com/index.cfm?".
          "fuseaction=user.viewfriends&".
          "friendID=" . $id;

$mech->get( $url );

my ($viewstate) = $mech->content =~ m/name="__VIEWSTATE".+value="([^"]
++)"/io;

# print "VIEWSTATE: $viewstate\n";

# Submit an dmove to page 2
$mech->submit_form( 
    #page => $url,
        form_name => 'aspnetForm',
        fields_ref => {
                            '__EVENTTARGET' => 'ctl00$cpMain$pagerTop'
+,
                            '__EVENTARGUMENT' => 2,
                            '__VIEWSTATE' => $viewstate,
                        }
     );

#print $mech->content;
[download]

Any idea what I'm doing wrong?

As long as you don't tell us what that "other error" with using ->fields is, we can't help you. The WWW::Mechanize documentation says to use fields:

    $mech->submit_form(
        form_number => 3,
        fields      => {
            username    => 'mungo',
            password    => 'lost-and-alone',
        }
    );
[download]

Personally, I would set the fields in the HTML form and then simply submit the form:

my $form = $mech->form_name('aspnetForm');
$form->value('__EVENTTARGET' => 'ctl00$cpMain$pagerTop');
... and so on
$mech->submit();
[download]

Reading the documentation, it looks like you need the field method.

I'm not sure what this has to do with headers though.