not all the video format can be played in ipod, you need to convert the video into mp4 or h.264 first. if you need to convert the video, you 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. i download this free ipod covnerter from their offical site. ---------------------
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. if you need some step by step guid, you can check this page.