I recently did some research, and judging on past Pokemon game releases, D/P might come out in the US sometime between February and May 2007. This is not at all a definate answer, but it should give you people a very rough estimate. I'm sure that games like Emerald, FireRed/LeafGreen and XD don't take as long to translate and ship as a complicated DS game does, but then again, D/P are very popular games in Japan, so the date is very, very vague. Expect it early 2007. I guess...
PS- This is not at all for sure. Don't anyone go posting saying that I claimed it'll come out on "this date" or whatever. Please don't.