I use Videora iPhone Converter, it has a lot of options (including automatically adding your converted files to the iTunes library), and it's pretty fast. Kinda processor intensive though. About 2 hours for a full length movie at high resolution, and about 10 mins for a 30 minute show at high res.
I'm on windows XP and I use PSP123, it's the same program my kids use to convert DVD's to their PSP. It converts the video to mp4 and I transfer it to iTunes. I don't know if you can download it online but they bought it at Target(in the PSP video games dept.) for real cheap and we all use it, it's super easy.