actually I think is the memory card (and/or swap file). If I take out the memory card, the MPlayer starts right away, if the card is in... nothing happens if I try to run the application. I have the memory card almost full with maps for maemo-mapper, over 200k of map tiles... maybe the MPlayer is searching for videos on the mmc and just take time (lots of time) until starts? If this is the case, can you disable the option to search for video files?
Now one more question, do the MPlayer works with the xm online satellite radio broadcast? I think they broadcast in wma format, and the mime is video/x-ms-asf.