Achivements between games (specifically Halo 3/Halo 3: ODST)

I sold my copy of Halo 3 a while back, without getting many of the multiplayer achievements.  Now that I'm playing ODST, which uses (what looks like) Halo 3's exact multiplayer, can I continue to work towards my achievements in the original Halo 3?
 
Also, are people in both games playing against each other, or are they separate game pools?
 
--Dave

Yea you can i got some recently by playing the ODST multiplayer disc :) 
 
and they are the same game pools