Dialga's at the top of MT. Cornet and the three others (Uxie, and the other two) are at the three lakes after you beat the league, there's cresselia in canalave, darjrai in canalave,heatran in stark mountain, and giratina in spring path
the legendary Pokemon in diamond and pearl are dialga and palkia.
No, a Bidoof cannot evolve into any Legendary Pokémon in Diamond.
Heatran
a lot of legendary Pokemon
Dialga
you cant unfourtanately
arceus
you can't catch it because you already beaten the legendary
no
you can't unless you have AR
Empoleon is not a legendary Pokemon. It is the final evolution of Piplup, one of the starter Pokemon in Pokemon Diamond, Pearl, and Platinum.
That would have to be Dialga.