How to shrink movie files for pocket pc?

hey all,
how can i shrink a movie file like avi,mpg etc… so it wont take alot of space and will fit on a pocket pc ? (dont have to be the best quality just resolution for pocket pc)
what progs should i use ?
plz help

Here is a software: http://www.dvd-software.biz/pocket_pc_dvd.htm
Nobody tried it yet, though.