why my iMAC monitor and external HD is continuosly warm?

Hi, I have a big inquire, I have an iMAC 27" monitor C2D 3.06 4gb ram, external HD, the upper back side of the monitor and the external HD are all the time warm, even if the screen saver and energy saver were working for long time when I come back it is still warm, even if I don't use the computer from one day to another (turned on)

This doesn't happen when I use windows XP with bootcamp though, when the windows is running and If I don't use it the external HD and the computer are cold for "logical reasons" (ie. I am not using it)

I have a widget application and the temperature is the following:

HD: 48º
CPU: 42º
ambient: 25º
GPU diode: 58º
GPU heatsink: 54º
Mem controller: 55º
Northbridge: 74º
Optical drive: 42º

I'd also like to add that I don't have any anti-virus application running on Mac, so I don't understand why the iMAC and the external HD are always warm like they are working??? although I am not using them??? Please help.

As a suggestion unmount the external drive as it may be causing your iMac not to sleep or the drive to sleep.