The potentially obvious issue is that you have my $mail_body = $template; in place of my $mail_body = $template->output; as documented in HTML::Template. I'm also not sure why you have CGI in there or where you are getting sendmail from (that's not MIME::Lite's interface), but perhaps this is more of what you need (does not run):

#!/usr/bin/perl

use strict;
use CGI qw(-oldstyle_urls :standard);
use CGI::Carp qw(fatalsToBrowser);
use Date::Calc qw( Add_Delta_Days Decode_Date_US Today );
use HTML::Template;

my $template = HTML::Template->new( filehandle => *DATA);

print "<h3>Email Test</h3>";


my $from = 'test@test.com';
my $to_name = 'Test Form';
            
my @mail_to = (               
             'me@test.com'
               );
    
my $subject = "TEST TEMP\n\n";

# template parameters

my $f_name = "Joe";
my $date = "02/08/2011";
my $acc = "123455667889";
my $company = "Test Company.";

$template->param(f_name =>    $f_name);
$template->param(date =>    $date);
$template->param(acc =>     $acc);
$template->param(company => $company);

my $mail_body = $template->output; # Corrected

sendmail( \@mail_to, $subject, $mail_body, $from, $to_name );

print "\nDONE\n";

__DATA__
<table width=\"100%\" border=\"0\" bgcolor=\"#ffffff\" cellpadding=\"0
+\" cellspacing=\"0\">
      <tr>
        <td width=\"100%\"colspan=\"2\">&nbsp;</td>
      </tr>
      <tr>
        <td width=\"100%\" colspan=\"2\"><b>Test</b></td>
      </tr>
      <tr>
        <td width=\"30%\">&nbsp;</td><td width=\"70%\">&nbsp;</td>
      </tr>
      <tr>
        <td width=\"30%\">Name:</td><td width=\"70%\"><TMPL_VAR NAME="
+f_name">.</td>
      </tr>
      <tr>
        <td width=\"30%\">EDate:</td><td width=\"70%\"><TMPL_VAR NAME=
+"date">.</td>
      </tr>      
      <tr>
        <td width=\"30%\">Acc:</td><td width=\"70%\"><TMPL_VAR NAME="a
+cc">.</td>
      </tr>      
      <tr>
        <td width=\"30%\">Company:</td><td width=\"70%\"><TMPL_VAR NAM
+E="company">.</td>
      </tr>      
</table>
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