YouTube to iPod is pretty tough. There are some Firefox add-ons that allow you to save YouTube videos to your PC hard disk but I don't know enough about the end result to know if they are cross compatible with iPods.
DVD to iPod can be done for free with a bit of Techy know-how, however if you want something "idiot proof" then I can highly recommend "CloneDVDMobile" by SlySoft which allows you to convert a DVD to a stand alone media file. I use this to create AVIs for my portable media player, but it also has an iPod file option as well.
You will have to buy a licence for it, but it works really well and so far my licence has allowed me free updates for 3 years.
NB If you don't own the DVD this process is technically illegal (Piracy), and I think copyright laws in the UK mean that you need to delete the ripped file within a certain time frame, however if you want to rip one of your DVD collection for viewing on tge train and then delete it once you are done, then I see no legal issues in doing this.