Why do I want to run a second X server on my desktop? So I can log in with another account without logging out of the first.

Edit /etc/X11/wdm/Xservers:

:1 local /usr/bin/X :1 vt8 -nolisten tcp
 ^                   ^   ^

Follow the example and add a second Xserver line. Change the dispaly id and the virtual terminal (vt) number (as indicated with carets).

From a virtual terminal (try Ctl-Alt-F1 to get to a terminal that isn’t under X) stop and restart the display manager:

service wdm stop
service wdm start
Poof, you’re done. And you have an ssh-agent available in each of your two sessions.

If you visit VT7 (Ctl-Alt-F7), you will get one X server login. You can log in to the other X server on vt8 (Ctl-Alt-F8).