According to VGCharts, this sold another half a million this week in North America, bringing its total sales to 1,107,754. (for North America) This figure is for the first eight days of sales.
1 million in American sales in the first week, brings total so far up to 6 million.
Also, in order to compare Japanese sales with Ruby/Sapphire: D/P is currently 800k ahead of where R/S was this far in release and selling about 3k more a week. Expecting 6.5 to 7 million Japanese sales isn't unreasonable (compared to 5.4 mil for R/S). However, its price will depend on American and PAL sales, which have a much smaller DS install base than the previous GBA one.
While their weekly numbers must be taken with a grain of salt, they're pretty much the only place to get sales data on older titles (under "world" then "software", you can get data on volume shipped if it passes a million).
Since they also list total console sales, it's easy to figure out what kind of attachment rates (ie, how many GBA owners bought Ruby/Sapphire, then figure out a %) for franchises, which tend to be somewhat consistent.
Also, regarding your Halo comments, keep in mind that this site is tracking worldwide sales. A series like Halo, while extremely popular in America, is nonexistent in Japan...a place where this game has already sold over 5 million copies.
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http://www.vgchartz.com/aweekly.php?date=39208