i am having the same problem. Had it when the files came from after effects as well to a certain extent.
But I created my slides in photoshop, 16 x 19, 300 DPI imported them into premier pro, and then created my show.
Looks great in preview window, once rendered or exported as avi file they look pixelated.
I looked for a way to check “uncompressed” under an avi file, and found only one way that made it a custom files and when I played it back only had audio. (CS4)
If you could try once more in detail to explain how you exported that avi file it might really help,. Thanks!