What software are you using to edit?
You need to render to the correct MPEG4 AVC/AAC codec. In Vegas there are 2 templates.
Audio: 128 Kbps, 48,000 Hz, AAC.
Video: 480 Kbps, 25.000 fps (max. 30.000), 320x240 auto-sized
Use this setting to create an MP4 file that you can sync to and play on Apple iPod.
and
Audio: 128 Kbps, 48,000 Hz, AAC.
Video: 1 Mbps, 25.000 fps (max. 30.000), 640x480
Use this setting to create an MP4 file that you can sync to and play on Apple iPod.