As no Mac can boot both Mac OS 9 and 10.6, there would be no point, but Mac OS X 10.6 doesn't support Classic anyway. If the 10.6 is a typo and you're using a PowerPC G4 Mac, it depends on which iMac model you have.
Theoretically, an external drive partitioned as APM can have both Mac OS 9 and 10.6 installed and bootable, but you'd only want to do that if you intend to use that single drive to boot both PowerPC and Intel Macs, and in most cases, it would make more sense to use an earlier version of Mac OS X for the PowerPC Macs.
Agreed--Classic is not a universal cure-all for running OS9 programs, so I also use a separate partition on my dual-bootable PPC Macs.
The problem I see you facing is that some 800 mHz iMacs shipped with both OS 9 and OSX and can boot into OS9; others shipped with OSX only and can only use Classic. Right now, the only factor can find that separates those that can boot OS9 for those that can't is the "OSX-only" version of the 800 had a fan and the dual boot versions did not--they were convection-cooled like the G3 iMacs
I found this info here:
They list three 800mHz iMacs and only two support OS9 booting.
If you find yours is dual-bootable, the only other item to worry about comes if you've upgraded the hard drive to something bigger than about 200GB: OS9 is only bootable from a partition that is under about 195GB. Easy enough to set up when you partition.
Good to hear from you after a couple of years.
Using EveryMac's serial number snipett feature I was able to determine my 800 mHz iMac is a order number M9105LL/A X Only model. Although I could never find this number on the computer, the fact that I could not boot up using a full install OS 9.2 disc supports the snipett conclusion. I guess I will have to stay with Classic.
Thanks once again for your help.