To enable or disable automount open a terminal and type gconf-editor followed by the [Enter] key.
Browse to /apps/nautilus/preferences/media_automount.
The media_automount key controls whether to automatically mount media. If set to true, then Nautilus will automatically mount media such as user-visible hard disks and removable media on start-up and media insertion.
There is another key /apps/nautilus/preferences/media_automount_open. This controls whether to automatically open a folder for automounted media. This key can also be set in the Nautilus (file manager) window. From the Edit menu in Nautilus select Preferences and then select the Media tab.If set to true, then Nautilus will automatically open a folder when media is automounted. This only applies to media where no known x-content/* type was detected; for media where a known x-content type is detected, the user configurable action will be taken instead. This can be configured as shown below.