use DateTime;

my $now = DateTime->now;
my $week = $now->week_number;

print $now->ymd," now (week $week)\n";

my $first = DateTime->new(
    year => $now->week_year,
    month => 1,
    day => 1,
);


print $first->ymd," beginning of the year \n";;

$first->add( weeks => $now->week_number );

print $first->ymd, " beginning of week $week\n";

$first->add( weeks => 1 );

print $first->ymd, " end of week $week\n";

__END__
2003-09-08 now (week 37)
2003-01-01 beginning of the year
2003-09-17 beginning of week 37
2003-09-24 end of week 37