Please review the archives of this mailing list. This topic has been discussed ad nauseum.
To wit: http://www.redhat.com/archives/fedora-list/2003-November/msg04078.html
... People really shouldn't be suggesting that users turn X tcp support on without noting that doing so is very insecure. X runs as the root user, and opening a TCP port may make the computer very susceptible to exploits.
Unless your machine is on a secure and trusted network, use ssh's X11 forwarding to run X11 applications remotely.
