samba or samba4?

[vichy]

Dear all:
I try to share my file/directories under ubuntu for xp to r/w.
But I have some questions/problems as below:
1. should I installl samba or samba4 and what are the differences?
2. I type my account and passwd under xp to connect to the
files/directories in Ubuntu, but I find I have no right to write. I am
sure that the username and pass is corret. Is there any thing in
unbutn I can see who connect in by samba and change the user's
authority?
3. when I edit the files located in ubuntu through xp, I will receive
a warning which saies my file has been modified outside.
have someone get the same experience before?
Appreciate your help,
vichy