How to capture the boby content of incoming mail with procmail?

Hi,

I'd like to copy the body of some incoming mails to a predetermined file.
How should I do this?

And More...
If I expected to receive standard emails with the following body (see 3 
examples) 
--------example 1-------------------
1 - messageA
------------------------------------------
--------example 2-------------------
4 - messageB
------------------------------------------
--------example 3-------------------
7 - messageC
------------------------------------------

and if each number means someone's code
and if I want to keep a list of the last (body) message from each diferent 
person
(and so the file should not contain more than one line starting with the same 
number)

how should I do this

note: I'm looking for a solution that just requiers changing the 
$HOME/.procmailrc file

Thanks in advance for your help

Lara

PS: Hope you understood the explanation... if not, please ask me for more 
details, ok?