Well here's one way to modify it (take advantage of CGI.pm's table generating capabilities, and use map -- don't wanna look at Date::Calc at the moment, maybe tomorrow ;D)

#!/usr/bin/perl -w
 
use strict;
use Data::Dumper;
use Date::Calc qw( Delta_Days Add_Delta_Days Date_to_Text );
use CGI;
 
my $q = new CGI;

sub date_range
{
    my(@date) = (@_)[0,1,2];
    my(@list);
    my($i);
    my $output = '';
 
    my $date;
    my %POS = (Su=>1, Mo=>2, Tu=>3, We=>4, Th=>5, Fr=>6, Sa=>7 );

    $i = Delta_Days(@_);
    while ($i-- >= 0)
    {
        push( @list, [ @date ] );
        @date = Add_Delta_Days(@date, 1) if ($i >= 0);
    }
 
    #build the matrix to hold the days.
    my @box;              #the arrray to hold the calendar data
    my $row=0;
    foreach $date (@list)
    {
        my $col = $POS{substr(Date_to_Text(@{$date}),0,2)};
        $box[$row][$col]= (@{$date}[2]);
        $row++ if ($col == 7);
    }



    ## for the header
    ##   is in here because array indices start at 0, not one
    ## and I didn't feel like modifying your code above (-1)
    $output.= $q->Tr( [
                        $q->th( [
                                 qw(   Su Mo Tu We Th Fr Sa)
                                ]
                              )
                      ] );


    ## gets warnings, since you don't init the array
    #$output.= join '', map { $q->Tr( [  $q->td( [ @{$_} ]) ] ) } @box
+;
    ## no warnings, cause i test for definedness

    $output.= join '',
              map
              {
                $q->Tr( [ $q->td( [ map
                                    {
                                        defined $_ ? $_ :" "
                                    } @{$_}
                                  ,]
                                ,)
                        ,]
                      ,)
              } @box;
}
 
print $q->header();
## since => is just a fancy comma,
print $q->table( &date_range(2001,11,1  =>  2001,11,30) );

## or for even "better" readability
print $q->table( &date_range(qw/2001 11 1/  =>  qw/2001 11 30/) );

__END__
Yielding the following:
[download]

Content-Type: text/html; charset=ISO-8859-1

	Su	Mo	Tu	We	Th	Fr	Sa
					1	2	3
	4	5	6	7	8	9	10
	11	12	13	14	15	16	17
	18	19	20	21	22	23	24
	25	26	27	28	29	30

 
___crazyinsomniac_______________________________________
Disclaimer: Don't blame. It came from inside the void
perl -e "$q=$_;map({chr unpack qq;H*;,$_}split(q;;,q*H*));print;$q/$q;"