Answering my own question! Hopefully if someone finds this in the future it will help.
I used the basic file from here:
http://www.iondev.lu/fckeditor/netnoi.txt
I found-and-replaced the "netnoi" with my own name, and uncommented the icon line to make an icon (16x16).
And the instructions on how to install it from here:
http://docs.fckeditor.net/FCKeditor_2.x/Developers_Guide/Customization/Plug-ins
Be sure to check that the plugins directory is correct -- in drupal the plugins folder is different than a default FCK install.
EDIT: Apparently the netnoi.txt has gone missing. Here is what I used:
/***
* Create blank command
*/
var FCKPixelCaps_command = function()
{
}
/***
* Add Execute prototype
*/
FCKPixelCaps_command.prototype.Execute = function()
{
// get whatever is selected in the FCKeditor window
var selection = FCK.EditorDocument.getSelection();
// if there is a selection, add tags around it
if(selection.length > 0)
{
FCK.InsertHtml('<span class="caps">' + selection + '</span>');
} else {
// for debugging reasons, I added this alert so I see if nothing is selected
alert('nothing selected');
}
}
/***
* Add GetState prototype
* - This is one of the lines I can't explain
*/
FCKPixelCaps_command.prototype.GetState = function()
{
return;
}
// register the command so it can be use by a button later
FCKCommands.RegisterCommand( 'PixelCaps_command' , new FCKPixelCaps_command() ) ;
/***
* Create the toolbar button.
*/
// create a button with the label "Netnoi" that calls the netnoi_command
var oPixelCaps = new FCKToolbarButton( 'PixelCaps_command', 'Pixels & Pulp Caps' ) ;
oPixelCaps.IconPath = FCKConfig.PluginsPath + 'PixelCaps/caps.gif' ;
// register the item so it can added to a toolbar
FCKToolbarItems.RegisterItem( 'PixelCaps', oPixelCaps ) ;