your laptop is too slow, and you should consider a new one if you're going to do multimedia stuff on it.

But anyway, with the sub-500mhz laptop, you should probably not bother with xvid/divx, and just use ffdshow. xvid's and divx's playback filters are both more cpu intensive than ffdshow.

vlc uses its own, to the best of my knowledge. If I remember correctly it uses its own implementation of libavcodec, and doesn't need other codecs to plug into it to play stuff. It's pretty optimized and pretty lightweight, so if you're having trouble at the point you are probably not going to have much success beyond it.

I think anime is pretty cpu-intensive in general, because of the bright, solid colors and clean motion. When a movie loses some information, you don't really notice because you wouldn't notice anyway. When anime loses the same information, you'll notice faster, so it has to lose less, and encode smarter, making it harder to decode. At least, so I think, I could be wrong.