No, you can only send Pokemon from your White to Black, Black 2 or White 2. Pokemon that you transfer to a Generation V game cannot be transferred back. Platinum can have pokemon transferred to White, if that's what you're saying; but be aware that once you do transfer them, you will not be able to get them back onto Platinum.
In saying that, I'm going to close this as your question has been answered and as this would usually belong in the Fourth Generation Help Thread sticky at the top of this board. Please use that next time if you have any other queries! :3
Closed.