Thank you for you answer Mike Odom and fermat7! I found 2 apps notes of ATMEL very useful for understanding the concept!
And yes, in the web there is a lot of info, plenty of them and very similar to what I am trying to do.
My intention is to usea arduino IDE so I'll probably use the ATmega328 with optiboot loaded so it can runs libraries of openenergymonitor.org.
I found this IC in similar applications on the web: ADE7753 . It is quite good for my purpose.
More details:
Finally I think I will only monitor the total power consume of the house, instead of the 3 or 4 circuits (kitchen, lights..etc)
With a CT sensor, a voltage sensor and the ADE7753 I will get all the information I need. I will control this ADE7753 with an ATmega328, which will also control an RFM12B transceiver. This would be a "whole" box next to the electrical "wardrobe"
Next to the router of the house there would be another "box". This one would be compound of another RFM12B that receives the info from the first "box", another ATmega328 and ENC28J60 ethernet controller that would allow to send the information to the web cosm. Ah, and probably and EEPROM or SD card to store the data received am I right?
I selected this MCU because I can load on them the optiboot uno that allows me to use arduino sketches.
It would be a prototype, so I will try to mount everything in breadboards (something it would give me problems...but well) If I had time and it works, the next step would be designing the PCBs.
About the power system for each box...here I have questions. What can I do? In the first box using normal AA batteries wouldn't be enough right? I Know you don't know the consume of every chip, but from your experience, what do you think?
And the second box, if is just a prototype, would I be able to supply 5V by the laptop?