You can set up a ftp server on the "file server" machine. Here is a free ftp server program:
http://www.pureftpd.org/
(and you can download the windows binaries at:
http://ftp.pureftpd.org/pub/pure-ftp...naries/windows )
You can also telnet into the machine to "remove control" it. I think there is telnet server function in the Windows XP Professional but as I don't use XP I can't tell you how to activate it.
there is also the Back Orifice 2k (
http://www.bo2k.com), it's known as trojan horse but it has actually no backdoors left (it's free software), just set the password.