i would say the smoothness of your animation would have to do with the amount of CVs you have in your curve - the more you have the smoother the animation would be...

but also hearing about the aliasing, i can't help but wonder if you rendered out to an avi file, the file is way too large, and you're just getting choppy playback (and didn't change the quality settings of your render)...

let me know if i'm right