Yeah you just cut a hole in the side of your case, with a sawsall, or sabersaw(dremals are for pansys). Drill a few holes or just super glue the fan to the side, plug it in to a power connector and your good to go. Make sure you throw away any fan gaurd that comes with it because its just something to block airflow. Don't worry if you have children because they will only stick their finger in one time.
Ok seriously now, cheap cases usually are setup for only 1 or 2 80mm case fans, but some of the higher end cases use 90, and 120mm fans, and have room for 3 and more fans. The larger the fan the slower it has to spin to get the same airflow of a smaller fan, slower a fan spins the less you hear it.