The problem is that OS 9 is designed to run on a PowerPC chip, and all of the Macs that support Boot Camp run on Intel (x86) chips. (For the same kind of reasoning, you can't just create a simple boot camp style assistant to allow you to install a Windows OS onto a PowerPC system -- it's just not the right architecture.)
What might work, if you really need to get that app running, is to use PearPC. The PearPC project works on emulating a PowerPC processor when what you're really running is an x86 processor. I can't say I've actually had anyone tell me they did this with OS 9, but there are other PowerPC operating systems it's been tested with (including OS X 10.3, which should then be able to run OS 9 apps in classic mode).
More information is available at
http://pearpc.sourceforge.net/
Keep in mind that when you're emulating an entire processor like this, the processing speed of the computer becomes a good bit slower. However, since you're planning to run software that was written for computers a good bit slower than the current generation of Macs, it may still run at an acceptable speed.
Alternatively, you could always look around the net to see if that particular program had any other fans who are already in the process of (or are already done) converting the app you want to use into an OS X native app.