I'm still confused, since I keep on getting different answers to this question. In the Milk Snake forum I got this reply to the same question:

Milk snakes are not king snakes. They are simply in the same genus. They are the milk snake within the Lampropeltis genus.
Genus - Lampropeltis
Species - triangulum (milks)
ssp - triangulum, syspila, etc....

The Lampropeltis getula species are the kings. They are related, but a different species within the Genus.

Just like the Elaphe (now Pantherophis) Genus....
within it you have the rats, corns, and fox snakes species and ssp.

Same thing goes with a myriad of other snakes like the Pituophis Genus - Pines, bulls and gophers. All related at the Genus level, but seperate species that are separated further into ssp.

Here is an eastern milk taxonomic break down for you....

Class - Reptilia
Order - Squamata
Suborder - Serpentes
Family - Colubridae
Genus - Lampropeltis
Species - triangulum
sub-species - triangulum

Hope this isnt too confusing