OOOOOOOOOOH! Finally! I've get known the problem!
My problem was the same of Absorbation! My firewall slows down the connections between my messenger and the server....
In fact if I disable it, My messenger works very good!
I thought that the problem was messenger plus cause before installing it, my messenger said me that there was an update for it, so I downloaded and istalled it. After I've installed Messenger Plus.
So, now I have another problem....
The firewall I use is the mcafee firewall 2005, and it asks me, every time a new program want a connection to the internet, if I want to allow it the full access, or deny it. I tried doing the advice of CookieRevised: I closed messenger, removed from Mcafee firewall the rule that admit it going on the net, and then restarted messenger. I don't know why, but with this program mcafee doesn't ask me if I want to allow it full access, but give it itself. And after that the situation doesn't change.
So now I don't know what to do. Should I free a specific port on my firewall, give it some specially settings....I don't know what to do!
Please help me another time