you can convert a .avi file in separate frames in photoshop. Otherwise, there is a software that exist and made just for boot animations (it convert your animation in the right number of images) I think its called avi to png ''something'' sorry I seen that last year so I couldnt tell but google will surely know the answer.
But before doing that, I hope you have learned and respected the timing sequence. The boot animation is a composition of ''60'' intro frames, followed by a ''50'' looped frames. (60 and 50 are just exemple numbers I dont remember exactly, you will haveto chek the real number of frames, you can do that in the boot anim changer software) What it means is that you have to create an intro which is simple, but the looped frames got to fit. The frame ''61'' has to fluidly follow last frame (60) of the intro. BUT the last frame of the looped got to be the same as frame ''61''. In other words your loop has to be perfect , and fit the right number of frames.