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[dosraider]

Depends on what you have downloaded ... can't you ask where you downed the game? They should know how to do this.

Anyway, I would say:
mount the folder with the install files as D: (cdrom)

mount d "x:\full path to folder\" -t cdrom

Install from D: on C: within dosbox.
(don't forget to mount your virtual C: )

Also: sure it needs to be installed or is it pre-installed? (ready to run in dosbox?)