If you could upload a video sample that might help.
If I need a good quality movie, I like to switch from avi to .png or .jpg and it will export a series of sequential images. I export them at 2 times the size I actually want the video. Then I shrink them all in photoshop using a batch command. Then I put them together using Adobe Premiere, but other software does it too.
But a small clip of your video might answer some questions too.
Chris