Ah, I forgot. You can have the tweaks included in the Designs Gallery by clicking the "Disc Designs" button on top of this gallery. Browse to where you saved the tweaks folder on your hard disk and open the folder. Even though you don't see anything, click "Add". Now, the tweaks will be accessible through the Designs Gallery.

To use them, drag and drop them on the MouseOff layer of the page on which you have an image gallery. You can change the settings by opening the Web Properties window and selecting the Placeholder tab.