Fragmented Video Stream in Preview Screen

I’ve made a DVD movie from a downloaded .avi file using Nero 6.6.0.19. It had my grandson performing to a song. Because the sound track had too much audience participation noise, I reduced the volume of the base audio track and added the song’s sound track as background audio. However, I had a hard time positioning the sound track to synchronize with the video because the preview screen in NeroVision Express 3 wouldn’t stream the video but only show a frame every 10 seconds.

Am I missing some setting in Nero or is this a symptom of an underpowered system? I have a Sony PCV-RX462DS Pentium 4, 1.30 GHz unit w/256 MB of memory and plenty of hard drive space.

P.S. I also have Roxio EVC 8 loaded and it does a full stream in the preview window.

Any suggestion or comment would be appreciated. Thanks.