Accessing Remote Computer Behind Company Firewall

Archived from groups: microsoft.public.windowsxp.work_remotely (More info?)

I am trying to access a Windows XP box from behind a clients firewall. I
can get to the following page http://ipaddress/tsweb/default.htm without any
issues. When I try to connection I get a error vbscript: Remote Desktop
Disconnected. However, I can connect from two other locations without any
issues; with the same laptop. So the only thing that is changing is the ISP
or outbound connection I am using. Two questions, can the firewall be
configured not allowing me to connect to the remote computer. And second,
is there a particular port I could use in stead of 80, or basically is there
a way to commonly spoof onto another service. These guys probably picked
all the defaults, and if I ask them to change something they will freak out
and not know what I am asking. But they will connect internally fine.