It still says to get arc2.tar; they haven't updated the page yet. Maybe it's because pg says, on Hacker news (http://news.ycombinator.com/item?id=634113) that it's a "preliminary release".
Personally, I'm using ANSI Common Lisp with Arc. I'd recommend it rather than On Lisp, as On Lisp is "a comprehensive study of advanced Lisp techniques" rather than an introduction. Maybe the tutorial is enough for you, but I quite like ANSI Common Lisp (so far).
So, while procrastinating from my Y Combinator application, I finished my arc implementation of Minesweeper. It's pretty basic, but in the spirit of "release early", here it is!
You can't mark spaces as bombs, and it doesn't tell you if you've won. It also doesn't ensure your first click is not on a bomb.
Start a game by calling (create-mines rows cols mines), replacing each starred variable by an integer.
Pick a cell to reveal by calling (pick minefield mask row *col), replacing each starred variable with an integer.
I'm fairly new to Lisp (and Arc), so if there's anything I could be doing better, please let me know. I'd love to hear your comments about this.