I currently have a PowerMac G5 2.5 Quad and after six years of reliable service, looking to upgrade to a MacPro 3.33 6-core. My questions lies on whether it may be possible to downgrade a MacPro to a lesser OS. The reason being is that I have PowerPC software that I may want to run. I recall my G5 coming with a certain version of Tiger and I had a slightly older version installed on an external drive. Trying to boot from it gave me a message that I needed to run the version of Tiger that came with the installer disc/preinstalled on the G5. From this, I'm led to believe that I couldn't go back to anything older and that it was hardcoded to prevent from doing so. The next OS, Lion, will not support PPC nor Rosetta. Since the current MacPro is a Snow Leopard machine supporting PPC using Rosetta, would a MacPro after Lion was introduced and came preinstalled with it be able to be downgraded to Snow Leopard? I don't need a new MacPro this instant and could wait until the next update which may happen towards the end of this year. If the downgrade would not be possible, then I'd buy a MacPro before Lion was released. Reading the Apple support page (http://support.apple.com/kb/HT2186), it appears that it can be downgraaded but some problems may arise. Another possibility comes to mind also. If I had an installer disc from a current Snow Leopard MacPro, I would think I could install it unless the preinstalled Lion MacPro is hardcoded to not allow it. Any thoughts?