Read the documentation, you have to convert your avi with vitualdub using the VP6 codec and have uncompressed audio at 16 bit, 44.1 khz. Then you can convert it with the EA VP6 Encoder.
I have an error, too. After I successfully converted my video, I put it in the movies directory as intro.vp6. After the EA sports intro, it shows the splash screens and hangs on trying to play the video. Is there a resolution or frame rate that the file should be? My resolution was 640x480, my frame rate was 24(23.976).