Messenger problems

[John Bell[_2_]]

So this is the situation. There are three computers in my living room, one is
a macbook, one is an ibook, and the other is a PC. The three computers are
connected to the internet via our wireless dsl provider. They all connect to
the internet without any problems.

But (part 1)

When I want to log into msn messenger with the macbook, I am unable to. I am
also unable to log into that account with mercury, adium (normally) and
jabber doesn't do too well either.

When I want to log into my msn messenger account with the ibook or the pc,
however, I have no problems.

(part 2)

Now, when I try to connect to my msn messenger with the MACBOOK using my
NEIGHBOR'S wireless dsl, I have no problems whatsoever. Adium and mercury
also connect.

Basically, this leaves me confounded as the problem seems to have to do with
the macbook and the internet server (or perhaps the local messenger server) -
and since my internet provider costumer service hasn't even heard of a
macbook, I get no help there. Is there anything I can do to solve this
problem? Can I configure messenger so that it can connect to a messenger
server manually?