after i installed 10.5.3 on my 08 mac pro, i couldn't boot without a kernel panic.
lucky me had a time machine drive in the system, so it only cost me 4-5 hours to revert back to my previous OS version.
you might have to archive/install.
funny that i've had to re-install or restore from backup Leopard 3 times on my mac pro, and my XP boot camp install has been rock-solid.
I think my mac is the best PC i've ever had. And it's better than my mac Mac.