$hash{00} is actuallay the same as $hash{0} because the key is a number and so is not interpreted as a string. if you would use warnings or the -w switch you would have spotted this one easier.
btw: i recently found out that $hash{1_000} is the same as $hash{1000} cos perl allows to use the underscore for legibility in larger numbers like 123_324_234.
hth
snowcrash