I got exactly your situation when I installed Leopard/Snow Leopard for my friend and I solved it:

Try to boot in safe mode with -x option

In safe mode, your display would always be 1024x768 and no QE/CL but it's just a temporary until you install a correct driver in a correct way, please check out http://netkas.org/?p=284

After install Leopard you can install Snow Leopard and find a driver + instructions for your graphics card

It seems Leopard doesn't have driver for 46xx, only Snow Leopard have

Beside iAtkos You can try iPC iDeneb XXX... for Leopard

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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 )