Other Resources on the Net
Since IONRadiant is based on the QERadiant editor (which is the foundation for many of the Quake2-based game editors out there), a lot of the functionality is similar or even exactly the same. Having said this, though, keep in mind that IONRadiant WAS modified by ION Storm during Daikatana's development, and so there will definitely be things in the editor that won't appear on general QERadiant pages.
The following are links to resources out on the web that refer to more general QERadiant operation. Some of these pages talk about "Quake 2", but you will still find answers for questions that pop up during your Daikatana editing.