It does not matter what OS you have. Unless the iPod is jailbroken, the only official way to put anything on the iPod is by using iTunes. The only official way to play any video on the iPod is to use built-in video player (I have no idea how it's called, but this is what plays video if you tap the Video or Movies icon). At some point VLC had an app there that could play anything, just as VLC on Windows, but Apple shut it down and threw them away from the AppStore (very helpful). The problem is, this built-in player is VERY limited in the choice of formats and codecs that it can accept. Basically, you can only use mp4 (or m4p, I think) files there.
So, you can download any number of apps that claim to convert video between anything normal - like DVD, xvid, divx, etc. - into files that iTunes can accept. If you have Nero, then Nero Recode can do that as well, although Nero Recode also does not allow many file formats. But, if you want to recode a DVD, then Nero will do it - provided it's not copyrighted (if it is, you'll have to rip it first, and I guess we're not allowed to discuss that bit). They have a built-in profile for iPhone/iPod, so you will get the right files. It even claims it can put files on your iPod without iTunes, but I never used that option, so can't say how it works.