Low power htpc & server

What is the lowest power cpu & motherboard combination for a home server but still work as HTPC too.

Thanks

Depends how many major cities you want it to power.

Could always look at an atom mobo and cpu and pair it up with a 4350 if you wanted hi def playback.
Or most likely a le-1640 and a 740g mobo.
Could use 1 stick of ram and a compact flash card - serial ata for storage.
Won't be fast, but will do as needed and use very little power.

E5200 and GA-E7AUM-DS2H motherboard actual measurements by me with an Aldi wattmeter thingy on the base unit power supply:

Built-in GeForce 9400 at idle: 41 watts
Built-in GeForce 9400 playing 1080p video: 51 watts.

Gigabyte ATI HD4850 at idle: 80 watts
Gigabyte ATI HD4850 playing 1080p video: 95 watts

Re. the Intel Atom, although the CPU is very low-power, the chipset needs a fan and is quite power-hungry. I can't remember seeing actual power usage measurements, though.