Well, it depends on exactly what level of animation you want.
If you want just some still pictures moving about, I would first make sure I had high resolution source files (300dpi or so) for each image, then scale them and reposition them in a fresh image for each frame of the animation. This will take a long time, as animation typically has 24 frames per second. You'll need a high-end image program to do this; I recommend The GIMP, as it's free and you can bind functions to keystrokes for quick functionality.
If you want moving pictures, proper animation, I'd cringe and back away slowly. Because that follows the same approximate approach, but you have to draw each of 24 frames per second. There are four timesavers I can think of here. First, there's the 'loop animation' so beloved of animators, where you animate one step of a repetitive process, such as walking along or throwing a punch in a routine. Second, there's the 'dirty animation' (which isn't dirty and is just a term I cobbled together from computer graphics concepts), where you have one drawing of a face and animate eyes and mouth onto it, ensuring the image stays steady and is quick to draw. Third, there's the 'flicker animation', which consists of two drawings of the same object, trying to be the same but not quite matching, and alternating them between frames, giving the image the appearance of slight motion. Fourth, there's computer animation; if you can get your hands on something like Poser or 3DStudio or (for free) GMax, you can build and animate 3D models; this is way harder than drawing stuff, but presumably saves time once you've spent a few months learning how to work it. I've used GMax and Windows screen captures (ALT+PRINTSCRN, paste into graphics program to trim) to string together a quick animation, even though the program isn't set up for it.
Any 'proper' animation will be way more time consuming than the already time consuming still animation. It'll probably be quickest to hire a few dozen Koreans to do it, like the big companies do. And take the Japanese approach of 'if you can save time by skimping on animation, do it'. Just so you know.
Once you've generated your frames (and they'll probably take up a lot of room, even if you keep the resolution down - 480x360 or some such is pretty good res for a movie file), you'll want to compile them together and add a soundtrack. I've only used one program to do this; I got it off
http://www.fileplanet.com a while ago, it should still be around somewhere. It's Platypus Animator or something. It's shareware and it works.
Well, that's my fairly cursory examination of the world of animation, which I know little more about. Hope it's helpful.
