It's totally unusable when flipping through many images.

Operating system: OS 10.6.5 - completely up-to-date. Clean install onto formatted HD. version 5.0.1

Model Identifier: MacBookPro1,1
Processor Name: Intel Core Duo
Processor Speed: 2.16 GHz
Memory: 2 GB
Boot ROM Version: MBP11.0055.B08
SMC Version (system): 1.2f10

Chipset Model: ATY,RadeonX1600
VRAM (Total): 256 MB
EFI Driver Version: 01.00.068

Other image formats work fine. Other apps open JPEGs instantly.
I had Tiger before, and JPEGs would load instantly.
My hard drive is healthy. Console doesn't show any unusual messages.

I tried turning QuartzGL on and off, system wide with the terminal command
sudo defaults write /Library/Preferences/ QuartzGLEnabled -boolean YES
I tried creating a new user account.
I tried copying from the install DVD.

Here is a screen capture I made of the problem: YouTube - Image preview in Mac OS 10.6

Here is a screen capture someone else did:
Here is him performing the same task with the same hardware in OS10.4:

I get mostly ignored on discussion forums.
Kinda disappointed and frustrated here.