I'm confused by your questions.
1) 33MB? You'd have a hard time encoding just SOUND for a full movie with 33MB.
2) Give this program a try. It's free. Make the program the size you want (250-500MB) and encode the audio at 80-92kps. Then set the "auto" function for the program, and stay out of the options.
http://www.fairusewizard.com/lang_en/index.html
This will create an .avi file, which you can save to a memory card (CF or SD) based upon which one you have with your X50. You should have an external card reader to copy files to your CF and SD cards, rather than using the ActiveSync connection. Then use BetaPlayer to open the file.
Have you downloaded the latest BetaPlayer (.095)? Don't worry about the word "unstable."
http://betaplayer.corecodec.org/