Normally windows can decode M-Jpeg files (usually files of that kind are downloaded from photo cameras). Probably the codec is newer. Try to install pegassus M-Jpeg codec. It never failed me.
As for MPEG2, I strongly recommend Elecard codec. PM me for other details over Elecard codec.
As for the source and MB problem. I assume you have a powerful computer, some P4 at 3 Ghz or Athlon about 3000 +. Usually they request a large amount of current on 12V branch. See the MB specifications about the 12 V amperage (maybe over 20 amps) and buy a power suply over 450 W but with more than 25 A on 12 V.
Sorry for my mistake, is pegasus, not pegassus:
http://www.pegasusimaging.com/picvideomjpeg.htm