use strict;
use Data::Dumper:

my($lease, %info);
while(<DATA>) {
  next
    unless (($lease) = /^lease \s+ ((?:\d+.?)+) \s+ \{$/x) .. /^\}$/;
  push @{ $info{$lease} } => { $1 => [split ' ', $2] }
    if /^\s+ (\S+) \s+ (.*);/x;
}


print Dumper(\%info);

__DATA__

lease 10.2.56.40 {
        starts 3 2003/08/20 10:37:28;
        ends 3 2003/08/20 22:37:28;
        hardware ethernet 00:20:af:52:12:0f;
        uid 01:20:af:52:12:0f;
        client-hostname "Telephone";
}
lease 10.2.56.75 {
        starts 3 2003/08/20 09:57:11;
        ends 3 2003/08/20 21:57:11;
        hardware ethernet 00:ef:18:ae:52:83;
        uid 01:00:ef:18:ae:52:83;
        client-hostname "beast";
}
lease 10.2.56.77 {
        starts 2 2003/08/19 21:13:05;
        ends 3 2003/08/20 21:13:05;
        hardware ethernet 00:02:95:9b:78:18;
        uid 01:02:0b:95:9b:78:18;
}