Windows Messenger roll-out

I am currently preparing to roll-out windows messenger within my organisation
and have a couple of questions:

Can we prevent people from seeing everyone else that has a messenger
account? For example, if we add the custumer service group so that they all
have a a messenger account, can we prevent them from seeing the IT personnel
who also are using messenger?

How do we determine or define what options are available during install for
the messenger client? Ie, who can use the application sharing option versus
just using chat?

What version of the software should we be installing? Are there known
problems with later versions?

Thanks,

Aidan Garnish