Due to the differences in hardware between older and newer computers, you cannot install an older OS on a Mac than the one it originally shipped with. That doesn't necessarily mean that the older OS wouldn't work, but you won't be able to perform the installation on that computer. I don't know if 10.6 will boot the new iMac and if it does I'd expect there to be performance issues and/or some functions (like WiFi) that doesn't work at all because of missing/outdated drivers.
If this were to work at all you'd have to find an older Mac, install Snow Leopard on an external drive and then see if the computer will boot with that external drive. (I doubt it but maybe) The only other solution is to find a copy of Snow Leopard Server which you can run using virtualization.
If the OP's desire to "maintain compatibility with other Macs on the networks" simply means to run PowerPC applications (that are otherwise unable to be upgraded to Intel compatibility), he should consider installing Snow Leopard (with Rosetta) into Parallels:
[click on image to enlarge]
NOTE: Computer games with complex, 3D or fast motion graphics make not work well or at all in virtualization.