A tool that I use sometimes to check my computer's fan speeds, read the temperatures of the motherboard and hard disk, read voltages and check the status of the hard disk using S.M.A.R.T. or SCSI attributes is SpeedFan. It is fully configurable and you can create custom events to handle every situation in an automated way. SpeedFan works under Windows 9x, ME, NT, 2000, 2003, XP and Vista. SpeedFan works fine on Vista 64 bit also.