As per my previous post about tools to use. If you want a very simple and powerful FREE tool. I think AnyVideoConverter is probably the easiest and friendliest to use. HERE
Just scroll down to the FREE version, download and install.
It looks like this:

It's very very simple to use. You can also use URL from Youtube and it will convert them to the mobile format.
If you want a bit more power for a small price ImTOO has a variety of encoding solutions that are also quite simple to use. SUPER is not so complicated once you use it for a while. I'll post a step by step process of how to work with SUPER to encode videos for Nokia Nseries in a future post. Until next time.
Keep on rocking!
El_Loco