I think its ok, to let the ogg-codec be seperate from the game-files, as its a "public" plugin. So you can use ogg, and put the installer for the codec into the "engine" folder.
The codec-installer is not counted (put it int the engine-folder) But the soundfiles are counted, and have to be in the game folder.
Any other custom dlls (like a render plugin etc) have to be in the game folder.
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you should include the ogg-installer and the d3d - dll in the engine folder, so someone without gamestudio has everything to install the game without searching for these public files.
You could also make a "meta" installer, that sets up everything automatically for convinience. But the 256kb game.zip must be manually openable. (and dont let the installer "sneak" gamefiles into the game)
Damn I'm in the hospital now So I'm not sure if I'm going to finish projects in time... (yes projects, cause I'm working on few little projects). But any way, I'm not out yet. 25 days are enough for me to get out of here I hope