getting user names with twapi

Hello all,
I´m trying to get the user names from several windows systems.
twapi::get_users -system $ip
I get a long list like this:
Administrator {SYSTEM1$} {SYSTEM2$} ....

I just would like the real personal users on the system. The SYSTEM1
or so have names like existing computers on the network. Why do they
get listed like users? Are they using network shares?

I would like to know a way to reliably distinct real users from
computers.
Would it be ok to say, a name with $ as last character must be a
system name?

At this time I loop through the list with hundreds of items calling
each one with twapi::get_user_account_info lasting an hour or so,
while there are only few real users on the system.

.