estaba leyendo de una web esto:
#5: Running multiple X sessions

* Difficulty: Easy
* Application: X

If you share your Linux box with someone and you are sick of continually logging in and out, you may be relieved to know that this is not really needed. Assuming that your computer starts in graphical mode (runlevel 5), by simultaneously pressing the keys Control+Alt+F1 - you will get a login prompt. Insert your login and password and then execute:

startx -- :1

to get into your graphical environment. To go back to the previous user session, press Ctrl+Alt+F7, while to get yours back press Ctrl+Alt+F8.

You can repeat this trick: the keys F1 to F6 identify six console sessions, while F7 to F12 identify six X sessions. Caveat: although this is true in most cases, different distributions can implement this feature in a different way.
de aqui:

sin embargo yo obtengo esto
~$ startx -- :1

X: user not authorized to run the X server, aborting.
giving up.
xinit:  No such file or directory (errno 2):  unable to connect to X server
xinit:  No such process (errno 3):  Server error.
sudo startx -- :1
[sudo] password for: 
X.Org X Server 1.7.6
Release Date: 2010-03-17
X Protocol Version 11, Revision 0
Build Operating System: Linux 2.6.24-25-server i686 Ubuntu
Current Operating System: Linux vaio 2.6.32-29-generic #58-Ubuntu SMP Fri Feb 11 19:00:09 UTC 2011 i686
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-2.6.32-29-generic root=UUID=9254bcc0-635c-4488-b3d4-d6d13b1abae4 ro quiet splash
Build Date: 10 December 2010  05:53:04PM
xorg-server 2:1.7.6-2ubuntu7.5 (For technical support please see 
Current version of pixman: 0.16.4
	Before reporting problems, check
	to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
	(++) from command line, (!!) notice, (II) informational,
	(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.1.log", Time: Sat Mar  5 17:58:51 2011
(==) Using config file: "/etc/X11/xorg.conf"
(==) Using config directory: "/usr/lib/X11/xorg.conf.d"

waiting for X server to shut down  ddxSigGiveUp: Closing log
si que funciona, pero me loguea como root, y eso es un problema, ¿que hacer?