Hello,
Looking at the information provided by the screenshots of Core Temp and CPU-Z, it's evident that you've got Intel Enhanced Speedstep Technology disabled (that is, throttling disabled), which is likely the reason for your high idle state temperatures.
Both Core Temp and CPU-Z are showing a current clock of 3166.7MHz (the stock speeds of the Intel Core 2 Duo E5400 processor) on idle load.
To enable Enahanced Intel Speedstep Technology, first it must be enabled in the BIOS (if it is disabled by an available EIST setting), and secondly, you need to make sure that your Power Scheme (Windows XP) or Power Plan (Windows Vista) is set properly. In Windows XP, choosing the default Power Profile named 'Minimal Power Management' will enable EIST. In Windows Vista, you need to change the advanced power settings of the active power plan so that the 'minimum processor state' under 'processor power management' is 5% or lower.
If in Windows XP, the default power scheme 'Minimal Power Management' has been erased, it will need to be created in command prompt using 'powercfg'. Entering the following (all one line) into command prompt will create a power scheme named 'Minimal Power Management' with the correct advanced power options to enable EIST in Windows XP:
powercfg /create "Minimal Power Management" /processor-throttle-ac "Adaptive" /processor-throttle-dc "Adaptive" /processor-throttle-ac "Adaptive"
You could actually name the power plan anything you like, such as 'Throttled' or 'EIST Enabled'. There are other parameters you can set which aren't available in Window XP's Power Manager. If you want more information about how to use powercfg, see the following article:
How to use Powercfg.exe in Windows Server 2003
See the following article for a illustrated guide to enabling EIST in Windows XP and Windows Vista:
Tech ARP - Reducing The Power Consumption Of Overclocked PCs Rev. 2.0