PaulS:
What a shame that you should have to be the one to RTFM. Surely, someone else should have read the f*ing manual for you.
Well, maybe I was misunderstood. I'm really noob with arduino and overall with electronic components... as well as writing in english 
I've read the overall documentation of RFNetwork on the Maniacbugs site, many times. There were many points not really understood by me. I've tried to read the datasheet too, but it's really difficult for me to deal with concepts I've never used before. C language is something new too, even if I've programmed with many different languages. (pointers, memory issues, aso.... uh!).
I think Arduino is really a great project to let people like me, who hasn't experience, to join a new world. The forum let us place in contact and help together. That I've not received useful hints to solve my issues in this case is a fact. No bad at all, because there is nowhere written here I can find all answers on my Arduino doubts Most of the time I've found many people helping me, that's great. After some months I went back to Maniacbugs site (library author) and found someone commented about the radio size limit. I've then read another time the datasheet and understood something new that I was not able to understand before. Well, in this way I've token more time but I'm more proud to have found a solution by myself Elementary for most of you, not for me.
Meaning someone else should read the manual for me and answer on my doubts was not my goal. If I ask something is 'cause I was not able to find exactly for an answer and is the reason why someone should ask on the forum.
Hope have clarified better my point of view and repeat my thanks to this great project and the whole community behind. Sorry if I've given another impression about that.
Simon