Xming

Если почитать по нему документацию, то можно найти там опцию rootless

http://www.linux.org.ru/books/lor-faq/lorFAQ-15.html#ss15.20

В том то и дело, что пересмотрел всю доку. У меня такой опции нет. Версия X:

Script started on Tue 10 Jul 2007 05:41:46 PM MSD
work:~# X -version
XFree86 Version 4.3.0.1 (Debian 4.3.0.dfsg.1-14sarge1 20050901212727 fjp@localhost.localdomain)
Release Date: 15 August 2003
X Protocol Version 11, Revision 0, Release 6.6
Build Operating System: Linux 2.6.8-16.0508-2 i686 [ELF]
Build Date: 02 September 2005

This version of XFree86 has been extensively modified by the Debian
Project, and is not supported by the XFree86 Project, Inc., in any
way. Bugs should be reported to the Debian Bug Tracking System; see
<URL: http://www.debian.org/Bugs/Reporting >.

We strongly encourage the use of the "reportbug" package and command
to ensure that bug reports contain as much useful information as
possible.

Before filing a bug report, you may want to consult the Debian X FAQ:
XHTML version: file:///usr/share/doc/xfree86-common/FAQ.xhtml
plain text version: file:///usr/share/doc/xfree86-common/FAQ.gz

Module Loader present
OS Kernel: Linux version 2.4.27-2-386 (horms@tabatha.lab.ultramonkey.org) (gcc version 3.3.5 (Debian 1:3.3.5-12)) #1 Mon May 16 16:47:51 JST 2005
work:~# exit
exit

Script done on Tue 10 Jul 2007 05:41:53 PM MSD

По всей видимости просто сборка старая :(

Xnest