Can Pokemon Diamond trade with white?

Answer 1

Not the way you think. Pokemon Diamond and Pokemon White can not directly trade with each other. Once you have defeated the main storyline, you gain access to new areas. Between Nimbasu city and White forest there is a small building. This is where you can transfer Pokemon form Diamond to White/Black. You need a second DS to do this.

Answer 2

No. You cannot trade Pokemon between White and Diamond. On your Pokemon White game you must go to the route in between Nimbasa City and White Forest.(Of course you need the National Pokedex) There you'll find a building where inside is a scientist person who tells you about his new transfer system. Then you need two DS's, one with your Diamond in it the other with White in it. On the DS with Diamond in it go onto DS Download Play. On White you talk to the scientist and then you play the little mini game and your Pokemon are transfered over. But sadly you can not transfer pokemon from white or black to any previous games because of the new pokemon. :)