ipods and PSP play the mp4 format like bob says. Nero Recode is a great program that will convert ripped DVDs into this format. So if you happen to have ripped a movie with something like DVDdecrypter, and run it through Nero Recode, it will format it for those devices.
Copies of it often come bundled with OEM versions of Nero on ebay for about a fiver.
I use HANDBRAKE to rip DVD's. Its very easy but takes a while. Once its finished you simply add the new file to your itunes library then select 'convert for ipod use' and your done. Like I said its very easy but just takes time.