If you wanna install Snow Leopard, you could use Empire EFI

The other way is that you need to install Leopard first then install Snow Leopard, after installing Snow, you can safely delete Leopard, installed Leopard is used for set up Snow such as creating DSDT, create customized USB install disc... You do not need to install Leopard first if you already have Leopard on a Mac. I've chosen this way because the first time I come to Mac OS X, Empire EFI or Snow Leopard haven't yet released

I would recommend other distros such as iPC, XXX v2, iDeneb... and burn it to DVD and try to install with different options, always -v to see what's going on, what stopped you
Other options you can try are cpus=1 ( rarely need, but in some PC when install Leopard, I have to use this to make boot possible ) or -x ( only if you can't boot normally )... you could try variety of combination of them

It's normal when your hardware specs can work with some but not the other distros, and it's usual when you have to reboot your PC and install HUNDREDS of times to find out the best install for your PC

I don't think there is problem with your graphics card because I've tried with 4670 4650

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10.6.2 Pcj 64-bit kernel | Mobo Asus P5LD2-VM Revision 1.03 945G/ICH7 Graphic Intel GMA950 | CPU Pentium 4 630 3 GHz HT
Sleep never wake up, Quicktime 64-bit crashed

10.6.2 Vanilla | Mobo GigaByte GA-EP43T-UD3L | CPU C2D E7500 | GPU GigaByte GV-N240D3-1GI Nvidia GT240 ( Full QE/CI )