The highscore.dat is pretty much a lost cause. The problem is every game stores it's high score in a different format. It's hard to read and hard to parse, and thus it's very hard to use it for front-ends, which I believe was it's intention.
Unless I am mistaken on this, the highscore.dat has nothing to do with saving your highscore. You see in order for a game to save it's score to the highscore.dat, it's game driver has to be coded that way. Since it is a lot of work for the devs to convert the highscores of a game from hex or whatever odd ball format the game uses into the highscore format, it is seldom supported.
Sorry