I am having the same problem...I got a SL disc tonight at the Apple Store, and it's version 10.6.3. All of my computers are on Leopard 10.5.7 or 10.5.8 (including my Mini 9) and I have no other Intel machine that I can upgrade in order to use NBI 0.8.4. I tried something I read in another thread, which involved replacing the old NBM in NBI 0.8.3 with the 0.8.4 version, then patching the mach_kernel with another found at insanelymac. Sadly, that still gives me a kernel panic when I boot from my USB drive--even with the supposedly correct kernel copied, it won't work. Any ideas, or am I stuck waiting for a NBI update that will work under Leopard?