This is a very minor tutorial but it's on info that seems to not be general knowledge.
Anyway, of you want to find ANY gpd number for any game on the 360:
-Go to www.xbox.com
-Search the game you need the gpd # for
-When you find that game and click on it it'll be in the url.
Ex: Need the gpd for halo reach
1) Xbox.com search for halo reach
2) Find it and click on it.. Loads this URL: http://marketplace.xbox.com/en-US/Pr...5-d8024d53085b
3) The gpd number is always the last 8 characters of the url.. In this case it's 4d53085b.
There it is, that's how you find a gpd number.