There aren't any English hacking tools formally released for Pokemon Diamond and Pearl, although one is in beta and another (well, several others) being designed as we speak.
In addition, as Gabe said, use the search form. For God's sake. I've got warned already for flaming someone for doing just what you did once already today. I really don't mind answering these questions, but they're stated so ineloquently...
I'm sure you'll be fine NIN. If you want to be involved, you can always simply spam HEX and test, test other people's editing attempts if you are close to anyone doing such, or provide us with graphics (spriting, for example, is a sure thing in Diamond and Pearl, where as we won't be needing tiles, due to the change from a majority of 2-dimensional to a majority of 3-dimensional mapping, and the obscene amount of shading they use in these games). If not, simply taking interest in a cause is supporting it, in this case, at least. I'm attempting to learn the basics of Visual Basic 6 in a week, so I can make some hacking programs with gabe_k's group. :) You're welcome to join me in learning a new skill, ha-ha!
Edit: As Gabe said, yes, a lot of the game is still based on tiles. But what I was saying is it's better to create something you know we can use, before creating an entire tile sheet for a map you'd like to build, and then realizing we'll never be able to use them, even after all hacking programs are built and operational.
Edit: Ahem... The thought came to mind you might not realize Gabe was being facetious when he said it was exclusive to Mandrake, etc... Yeah.