if you only open the m2v in MPC, it will not in sync, it's normal and notings you can to.
( this's the way MPEG-2 splitter/DirectDraw handle the m2v files :-( )
if you need to check the srt in sync with the audio, you can try this program

Aegisub, it supported UTF-8/BIG-5

you can load your srt file, then load the audio file. you don't need the video part for this time
check the sync, if all OK. you can convert the srt -> sup/son
and mux it with the m2v/ac3 :-)