not all the video format can be played in ipod, you need to convert the video into mp4 or h.264 first. i recommend you to try this free tool called leawo free ipod converter. It is completely free with no watermark. you may have a try. Inputs: WMV, WMA, AVI, MPG, MPEG, RMVB, RM, RA, MOV, QT, MP4, M4V, DV, DAT, MP3, AAC, etc.
Outputs: iPod MP4 video, iPhone MP4 video, Apple TV MP4 video, MP3, M4A, WAV, AAC, etc. you can download this free ipod converter here--------------------
For windows: http://www.google.com/search?hl=en&newwindow=1&q=leawo+ipod+converter&aq=f&aqi=&oq=
For mac: http://www.apple.com/downloads/macosx/video/leawomacvideoconverter.html
wish help and good luck. and i think this step by step guide may can help you too.