Question: How do I enter Spanish characters (or other special characters) into the puzzle?
Answer: For MS-Windows systems, you can enter ALT, followed by a number, to get special characters. This is rather system dependant, but could work for your needs. See: http://www.samiam.org/typing.spanish.characters.html for more details. The basic idea is that if you can get a character into the web page, it should come out in the generated puzzle. (Thanks to Dr Fran Dorward).
Another choice is to copy and paste from the Alphabet chart.