Poppies are much easier to start in the open field of a vegetable garden than among the shadows of a perennial garden. The lore in my part of the world says to throw the seed out onto the snow in early spring. I find that when I order poppy seed, I get such a stingy few in the package, that it makes sense to sow it out in the open, where I can babysit the seedlings.
Once you do get poppies, however, you will have them forever, because each flower produces a ton of seed and disperses it with one of nature's more ingenious pieces of engineering. The big pods are like a salt shaker or sugar caster, with a ring of neat little openings below the flat top, out of which seed flies every time the pod blows in the wind or is brushed against by a gardener.
Despite the density with which poppies will produce seedlings, the seedlings have to be ruthlessly thinned if you want them to look like anything. Otherwise, you will get pathetic, tiny flowers at ankle height. Given enough room, on the other hand, each plant can grow waist high, with wonderful blue foliage and incredibly seductive fat buds.
As to the legality of this display, from which opium could in theory be produced, I've never attempted to stay current with it. Twelve years ago Michael Pollan wrote a brilliant essay on the subject, available at the link. This is the highest form of garden writing–the kind that happens to be talking about the culture while it talks about plants.