Originally Posted by Taisto

Boot into leopard, copy the mach_kernel.test7 file to Your 10.6 root folder, open terminal and set permissions :

sudo chown -R 0:0 mach_kernel.test7
sudo chmod -R 755 mach_kernel.test7

Restart. While booting, press F8 if needed, and in prompt enter "mach_kernel.test7" to boot using the new one for sure. If this works, You can edit boot.plist file and change kernel to .test7 there - this way it's easier to avoid problems with updates etc. cause You always have Your working kernel untouched.