IPods only supports videos that are in the AVI format which means that you need to convert the mp4 videos into AVI files format. There are different software's available in the market like my video convertor that can convert the videos. Then load the videos onto iTunes and sync the computer to an iPod to download the videos onto the iPod. Visit http://www.ehow.com/info_8198591_can-movies-itunes-ipod-touch.html for more information.
iPod touch 4G will only support MP4, you can use a program like youtube downloader to convert any format to MP4. Then import to iTunes and sync. That simple and without costly programs, you can do it all.