Yeah, it works!
I did this: "I typed docastle in the search box on the site you listed and it came right up with a file for Mr. Do's Castle (set 1). Downloaded it and placed the ZIP file in the ROMs directory, ran an audit on the games and it worked when I selected Mr. Do's Castle (set 1) from the list."
And it worked. I guess I got lucky with the Mr. Do you offered. I also went to the preferences and pointed EVERYTHING at the ROMs folder...dunno if it helped or not, but it worked
I went back there, hunting for more games, and many of them so far, don't work. I also can't seem to get the sound working on Star Castle or Armor Attack. But, Phoenix worked, and so did 1942, and another old fave, The End.
Well, MAMEOSX is working, not perfectly, but it's working. That giant list it comes with is a pain. I can't say for sure what made it start up, as after Mr. Do worked, then 1942 worked, too, afterwards
Thanks to everybody here
It's still really user unfriendly