Because the arrangement of the pieces for both sides are 'mirrored',
that
is King on left, there should be no difference who moves first... Some
old
literatures put Black at the bottom (ie. move first) but the 'official'
rules (probably written quite recently and followed the Int'l version)
now is that White moves first.
And, by the way, I would like to add that there is a new ThaiChess
software with nice graphics etc. at www.thaichess.com... Check it out!
at about US$5, it's a great value and fun. (The program incorporated
ALL
drawing rules, the first one that I know of)