I've found a very nice application that is called Smartmovie. It lets you view movies on almost every portable device. It work on palm, but unfortunately on palm with high resolution screens. I've written a mail to the software house asking if they are planning a treo 600 version. They answerd me back that a treo version will be released very soon. So give a look:
http://www.lonelycatgames.com/

Dose anybody have experience of this application on other devices?