my %period = (
    Jan => ['01 Dec','31 Dec'],
    Feb => ['01 Jan','31 Jan'],
    Mar => ['01 Feb','28 Feb'],
    #...
    Dec => ['01 Nov','30 Nov'],
);

my $curr_month = "Mar";
my $curr_year  = 2010;

my $p = $period{$curr_month};
print "$p->[0] $curr_year - $p->[1] $curr_year\n";   # 01 Feb 2010 - 28 Feb 2010