Open up terminal and type the following command
iconv -f ISO-8859-7 -t UTF-8 windows-subtitle.srt > mac-output-subtitle.srt
where windows-subtitle is the filename of the subtitle with Greek characters you want to convert and mac-output-subtitle is the filename of the mac playable subtitle, so you want watch your movie with VLC , mplayer or any other subtitle capable player.
Of couse you can always WATCH IT WITH QUICKTIME which supports directly Window’s Greek Subtitles !!!!!
