[Myrddin]

The hash stored for your password isn't aware of the size of the input that generated it. The rainbow table simply provides an input that the md5 will transform to the given has value. It's a matter to trading space (storage of values) for compute time. The md5 hash is a one-way, so you have to cook up tables of values that will produce the desired result.

[DaveA37]

Crippling the internet might not be the worst thing to happen.