Making up masks for v.1 is a pain in the butt.
You need to find the 001defaultmasks.mov file in the mask directory and make a copy of it. Store the copy somewhere safe.
You will need to make your shape up in Illustrator. Use no stroke and fill the shape with black. Save out as an illustrator file.
Open After Effects, create a new composition. The composition needs to be 512 x 512. Make the composition as many frames as you need. Import your image into After Effects and place it in the composition. Set the background to be black. You can't see your image, right?
Toggle the alpha channel button on the canvas window.
You can then do funky things with it if you need to. The important thing is that when you render the movie out, it needs to be Animation Codec and RGB + Alpha. You'll need to render it out as 001defaultmasks.mov and place it in the masks folder in Cat v.1.2 and start the application. You can also link your original mask movie and plonk the new mask movie together if you wish. Easy to do in Final Cut Pro or even QuickTime Pro.

Let me know if you need any more help.

Hugh