How do you see number 51 and 52 on the Sinnoh pokedex in Pokemon platinum?

Answer 1

51 and 52 are Cascoon and Dustox. Wurmple can evolve into Silcoon (thus into Beautifly) or Cascoon, and then into Dustox. It's set for each Wurmple, but there's no way to tell til it evolves.

Catch a bunch of Wurmple, and evolve them. One's bound to become a Cascoon.