Right its a big subject, but heres some links to help you out.
http://divx.ppccool.com/ This is a really simple to use video encoder, you can set everything up quickly and convert videos to a nice small file size.
http://pocketmatrix.com/guides/index...d42c24f6c6999b
There are two guides here that run you through ripping a dvd and converting to your pocket pc. What you can do is just follow the ripping guide, then use Pocket divx encdoer(above link) to convert the video to your pocket pc.
To play Div x and xvid files its worth getting Picards Betaplayer Its feee and very very good :)
http://betaplayer.corecodec.org/