Hello Lauri.
The Sudoku program lets you switch from Numbers, to Letters, and back - even midway through a puzzle. You can even print the puzzles out with Letters instead of Numbers.
Is that what you mean by Letter Su Doku?
To read more about the program, visit
www.sudoku.com/program.htm or you can download the trial version of the program from
www.sudoku.com/download.htm and use it free for 28 days (you would have to buy it to keep using it after that).
- Wayne