there is a certain flower and it acts like the grisseuos to giratina. i dont remember what flower it was. but if have heartgold or soulsilver, you take shaymin to the flower shop in goldenrod city, and make sure shaymin is outside its pokeball. when you walk in she will tell you, shaymin is cute and then she will give the flower.
you can only get it in platinum and talk to a woman in floroma town and with shaymin on your team and you will get the glacidea flower
bring a shaymin to lucanosa town and talk to the lady under the bridge and she will give you gracidia buds
Shaymin doesn't evolve, but you can change it's form by using the Gracedia flower, which can be given to you by a girl in Floraroma Town if you have a Shaymin in your party.
Although Shaymin doesn't evolve, it does have two different forms.
shaymin is special because it can change forms with the graicidea flower
There is no evolution. But you can change its form into a skaymin. (Sky Shaymin)
Shaymin does not evolve. The alternate you see that is advertised for Pokemon Platinum is a different form of Shaymin, just like the alternate forms of Deoxys.
Sorry, but Shaymin can only change form in Platinum.
no shaymin's sky forme is exclusive to platinum
Yes, you can change Shaymin while it is in Land Forme over to its Sky Forme in Pokémon White however you will need the Gracidea in order for it to change it forms. You can get the Gracidea from a character in the Lacunosa Town Pokémon Center.
You can't change Shaymin into Sky Form in Pokemon Diamond (that includes pearl). You can only change Shaymin into Sky Form in Pokemon Platinum (that includes Heart Gold and Soul Silver). You can get the Gracidea to change Shaymin into Sky Form.
I think that shaymin's forms are exclusive to platinum as they require a giveaway from a Nintendo event. If it wasnt built into platinum pearl/diamond then you wont be able to change its form. It would be like trying to trade across Pokemon to lower generation games which don't support that Pokemon. If the method for doing it in platinum doesnt work then you simply cant do it.