I have found an excellent plugin for the myBB software that allows the administrator to create custom input fields for posts. It's extremely configurable, with many options.

(begin techno-babble)
In case anyone is interested, myBB is written in PHP and stores all it's data in a mySQL database. The plugin is just additional PHP files uploaded to the right place. Then, automagically, all of the plugin's configuration menus show up in the online administrative control panel just as everything else is. The data from the custom fields is also stored in the MySQL database, and recalled when a message is read. The plugin has many options, yet allows even further customization, which I took advantage of. A few edits to the templates and everything was looking great. (I had to learn some XHTML and CSS, big deal... which reminds me, myBB pages are 100% XHTML 1.0 valid per the W3 consortium validator)
(end techno-babble)

Anyway, I've been able to recreate the quake prediction input forms that Earthwaves currently has. Right now they are active in "Test Forum 3". If you would like to see what the result looks like, I made some test posts there. If you have an account and log in, you can try posting a practice prediction yourself. (don't post legit predictions, no guarantee they'll be saved down the road, still configuring the software)

The forms only show up when you make a new post. (must be logged in, of course)
They only show on new threads, and not on replies.

Some fields are required, such as Minimum Magnitude and Maximum Magnitude. Several fields already have default values in place. You may change them as needed to fit your prediction's needs. For example, if your prediction is for a mag 6.5 and larger quake, you set the minimum to "6.5" and leave the maximum at "10.0".

Also, some of the fields have range checking enabled to help ensure you don't put numbers in that make no sense. An example of that might be mixing up your latitudes and longitudes and trying to put a longitude of -118 in the latitude field instead.

Please take a look and let me know what you think.

Brian