I've done the update downloading the dmg from apple (check SHA1 cause it fails many times) and installing just like on an intel pc. I could do that cause I had voodoo kernel and the disabler kext. Voodoo installs itself as mach_kernel.voodoo, so it isn't overwritten by the update, also I don't use any modded kext (except for the ps2 fix that I had to reinstall) Disabler takes care of appleintelcpu.... and that's all I think.
Anyway you should do a backup just in case.

Good luck!

EDIT: once you got it running you should restore system and seatbelt kexts from a 10.5.5 installation. System kext is included into voodoo's installer and I can send you 10.5.5 seatbelt if you want.

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CPU: AMD Athlon 64 3000+ @2.3Ghz - Motherboard: ASUS A8N-SLI nForce4 SLI - nForceLAN by eno - SuperNForceATA by Medevil - RAM:2 GB DDR 333Mhz Audio: ALC850 Video: XFX nVidia GeForce 8400GS 256Mb (0x06e4) QE & CI from Chameleon 2 RC4Ethernet: Realtek RTL 8139 Series (working out of the box) OS: Snow Leopard 10.6.4 (aryajuanda's guide) + Windows XP 64bits