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Err, don't quite understand your first question but if you're asking whether the placement of fans have anything to do with its cooling ability then, yes!, the fans should be placed blowing directly over hotspots or stagnant airflow areas in the case and generally at the back and front ends of the casing so that the air they draw move in an unbroken streamline over the CPU and chipset for max. cooling. They can be mounted directly overhead the CPU by cutting a hole in the side panels or as a 'blowhole' by cutting a hole at the top. One fan blowing in and one fan blowing out helps if the innards of your case is very 'messy' and obstructs the flow greatly but the flowrate is that of just one of the fans, but two fans sucking or blowing out together provide great airflow if there's enough openings in the case and if the IDE cables have been folded neatly, etc.
Don't know about DVD-ROM drives but CD-ROM drives can sometimes overheat until the disc currently in the tray becomes temporarily unreadable due to heat warping. Good case ventilation is recommended.
