As I don't believe there is a version of Mobile PC that comes with Australia maps (correct me if I'm wrong), the Australia maps you added are not locked. A locked map needs a device to unlock to and Mobile PC doesn't qualify. If you had the version that includes the GPS, you unlock the map to that GPS.
To insert an image, you need to use the 'Go Advanced' button below your reply window. That will present you with an 'Additional Options' header containing a 'Manage Attachments' button. Click on that and upload the appropriate image from your computer.
If you need directions on creating an image, we can probably help you with that too.
Terry