iPod can only play video files in MP4, H.264 format, If you have some wmv movie, and you want to play it on your iPod. Then, you need a software to help you convert wmv to iPod compatible format, just convert WMV to iPod Touch/iPod Nano/iPod Classic as follows:
The Tool We Will Need:
A WMV to iPod Converter – Video Converter Ultimate (Windows 7 Compatible)
Video Converter Ultimate is an easy-to-use WMV to iPod MP4 video Converter which can convert WMV to iPod video with high quality. Moreover, it is a full-function video converter which can help you convert video to other video formats like AVI, MP4, MOV, MPG, WMV, ASF, 3GP and so on with smart editing functions.
Note: if you want to convert WMV to iPod on Mac , you can refer to Video Converter for Mac here.
Download Video Converter Ultimate, install and run it. then import WMV video by "File" button or File on menu bar.

Choose .mp4 as the output format to fit your iPod touch, iPod nano, iPod classic. The default setting will work great, You are also allowed to customize the output setting such as resolution, frame rate, bit rate, etc by clicking "Settings".

Note: Video Converer provides smart video editing functions like Cropping (cut off the black edge of movie), Clipping (trim your favorite segment of video to convert), etc, you can DIY your WMV video before WMV to iPod Conversion.
Hit the big blue "Start" button to convert WMV to iPod MP4 video.
Within a few minutes, the converted WMV videos are ready for your iPod touch, iPod Nano, and iPod classic (click "Open Output" to access the converted files directly).
Follow below steps to put music Video on iPod:
1. Open iTunes, find your converted video on your hard drive, and drag the video to your iTunes library, or click iTunes "File -> Add File to libs" and import your video to iTunes.
2. Connect your iPod to computer via USB cable, when your iPod is detected by iTunes, iTunes will sync the video music to iPod automatically
If you don't like to use iTunes to manager your iPod Media files, you can try iTransfer instead – which can copy music video between iPad/iPhone/iPod to computer directly without iTunes