for the wifi I have no idea, but for the X session maybe I can help.
If I well remember the justX flavor should start an X session by default. Maybe you started it once in text mode (option screen=text passed to Grub) and now you are experiencing the same problem as http://forum.slitaz.org/index.php/discussion/1068/lancer-lxde/ Can you check this? If it is not so, can you check the logs in /var/log/? If there is one file /var/log/slim.log it probably means that slim aborted for some reason which might be explained there.