You can write your game using any language you wish and for any operating system you wish. However, your entry must receive ten votes for it to be eligible for any prizes, so you need it to be playable by as many people as possible. For this reason, you should use a language designed specifically for IF, such as TADS, Hugo, Inform, or ALAN.
There are a couple of things which you need to keep in mind when writing your game. Judges will only have two hours to play your game; if you write a long game, many people will not see parts of it. You may not base your game on works currently under copyright without permission from the copyright holder. Your entry cannot have been released previously, and you must be willing to release it as freeware or public domain.
If you have the stamina for it, you may submit multiple entries, so long as all of your entries meet the above requirements.
As your game nears completion, you should have it beta-tested by several different people if at all possible. Lucian Smith and Liza Daly have set up a web page for authors who need beta-testers. You should also write a complete text walkthrough for your game and submit it with your game. This will allow me to insure that your game is winnable before releasing it, and will let judges skip difficult puzzles if necessary. If you wish, you can submit a walkthrough for my testing purposes but not for general release to the judges.
To enter, you must mail me with your intent to enter by September 1, 1999. You must also send your game to me by September 30, 1999. The simplest way would be to mail me your game as a uuencoded or mime-encoded attachment.
This year's organizer is Stephen Granade.