basically, according to intel spec sheet, c2d uses 65W of power. just add that with the total power usage of all other devices, board, hdd, optical drive, fan, graphic card, etc, then u'll have an idea whether that psu is sufficient to power up ur pc. of course, efficiency is another issue.

if ur psu isnt giving stable voltage readings, try cool it down with extra fan, or better airflow. in most casing, the psu acquires hot air from within the casings, so it have problems cooling down.

if u r using too much devices, then u'll probably have problems.. fan running loud and quite irregularly, fail dvd burning, etc.. or worse case, blow up the psu.