Backup computer for 10.6

We currently have a MacPro Server running 10.6.x and want backup hardware that we could grab and immediately throw our current boot drive into in the event of a hardware crash. Our machine is a 5,1. I -think- a new machine would not boot from 10.6.x. Can somebody confirm that and possibly let me know what will actually boot from 10.6.x ? I know that Apple may give a "recommended" response as opposed to a reality based response so I thought this might be a good place to check. If we could boot a little Mini from an external drive that would be great but I do know that Apple has said that would not be possible. Whether that is a company line or whether the mini would indeed refuse to boot the Server version of 10.6.x is unknown to me atm. I know we can simply go out and find a used 5,1 machine and all should be well but I'm curious about other options. Thanks in advance.