If you use gdm:
1- Hit Alt+Esc to bring up 'run everything' and type - ne lo -
That will bring up a icon called 'New Login' which will start a a new x server with gdmflexiserver.
2- Add the new login icon to your drawer/itask/itask-ng
3- Run gdmflexiserver from a terminal
If this doesn't work check if gdmflexiserver is installed in synaptic.