Q: Unable to Boot Into Mac OS 9.1 CD for Dual USB Snow iBook G3

The Dual USB iBook G3, if that is the model name will only take the discs that shipped with it new, and the discs that look like this with the 9.2.1 stamped in black on one side without Update, Dropin, or OEM written on them.

To verify you have that very model, see this tip:

iBook: How to Identify iBook Models - Apple Support

If you have a different model, this tip explains which Mac OS 9 disc will go with them:

Mac OS: Versions, builds included with PowerPC Macs (since 1998) - Apple Support

White discs exist for:

9.0

9.0.2

9.0.4

9.1

9.2.1

that are full release non Update/Dropin/OEM.  No Mac may use an older disc than shipped with it.

Note some iBooks are too new to use any white Mac OS 9 disc (if they shipped with 9.2.1 or later), and can only use the disc that shipped with them.  Hard to get, although occasionally possible via AppleCare or places that sell used or refurbished Macs*:

http://www.macmaps.com/usedrefurbished.html

* Links to my pages may give me compensation