Styl: The best thing to do is to look at an existing animated skin to see how it's achieved. Basically you just make your animated titlebar like any other animation,(multiple images) and then when you put it together in skinstudio, you specify the amount of images in the titlebar and also in the left, right and bottom images.
One thing to remember....if you have 20 images in your titlebar animation, then the left, right, and bottom images must have the same amount of frames even if they are not animated.
I have only released one animated skin, it's called "Cogs", and it has a simple animation in the titlebar. If you download it and then look at the titlebar images using an image viewer,(I use ACDSee) you will see how it works.
DISCLAIMER: There are people who can describe the process a lot better than I can. (I'm just an artist, Dammit [tm] )