Ok like many people I had the dreaded "can't find mach_kernel" error after a failed install, this stopped me from attempting the install again.
Here are a few things that may eradicate the problem:
1. Are you using the retail copy of snow leopard? It may be a bad image of the disk.
2. Is the USB device your using able to perform the install.
3. TRY AND USE A DVD DRIVE!!!!! THIS SOLVED MY PROBLEM WITH BOTH THE INSTALL AND MACH_KERNEL ERROR!!!
I know this may not help many people but it's just for people like me who are new to hackintoshing.