if you look at this guide
http://www.aximsite.com/boards/showthread.php?t=3970 then you can change the demensions to what you want...
also note in this guide
http://www.aximsite.com/boards/showthread.php?t=44591 you could change the output dimensions also
and in Pocket DVD Studio (not free but very automatic) there are many modes including 640x352