First goto:
Control Panel » Gallery Settings
verify the settings are what you want.

Then goto:
Control Panel » Forum Settings
Select the tab at the bottom to add a new forum.
you want to enable the folloing field:

Is Gallery Forum?

You may not toggle the gallery status of a forum that has already been created.

Then you need to goto:
Control Panel » Forum Permissions
Switch to your new gallery forum.
Edit the following permissions
Total # of gallery images
Maximum size of gallery images (enter this value in bytes)

Blue Man Group
There is no such thing as stupid questions. Just stupid answers