I've created boot package following the instructions, but upon booting the USB disk I got KP.

No matter what options/kexts I choose I get KP, but I will not be trying any more because I'm able to install SL using other methods. I do get KP also, but not during the install, I got KP when booting installed SL.

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AMD Athlon X2 550
Gigabyte UD4P 790fx
8Gb DDR2 RAM
Ati Radeon HD3850