*_* The magic words have been said.... huu huu huu....
Indeed, Avisynth is good stuff. I'll admit, though, there's no guide I've actually seen to make AMVs directly from Avisynth. Fortunately.... you have someone who's had some experience.
A word of caution, though: Avisynth does have a bit of a learning curve. On top of that, there's no GUI... everything you do, from a resize to a crossfade, is written into a text file. It takes a lil while to get used to the syntax.
On the upside, though, you have incredible precision over what you want in your video. Literally, precision down to the frame level that's 100% reproducible.