1. Go to Main Menu -> Preferences -> Network Connections click on Add and choose Wi-Fi. Choose a network name (SSID), Infrastructure mode. Go to to Wi-Fi Security and choose a WPA/WPA2 Personal and create a password. Go to IPv4 settings and check that it is shared with other computers.
2. Do sudo vi /etc/NetworkManager/system-connections/YOUR_CONNECTION_NAME and change mode=infrastructure to mode=ap and save it.
3. Click on Network Manager near clocks and choose connect to hidden wireless network –> choose your connection –> enjoy.
P.S. If it does not work, run iw list and check in Supported interface modes: * AP, if you do not have AP there, probably your Wi-Fi card does not support this mode.
(Quelle: http://community.linuxmint.com/tutorial/view/1832)