Matt, if it works well with safe mode, it points to a driver issue. Try disabling in your BIOS (is it up to date?) devices that are not essential for booting (LAN card, USB, audio card, for example) and see if it goes away. Then enable them one at a time to see whcih one is causing the problem.
I saw you have onboard video. It might be worth trying boot without your GeForce 8400, using just onboard, to see if the problem persists
Regarding Intel chipset, I would not rely on the search programs, check at the Intel site: Intel® G33 Express Chipset - Intel® G33 Express Chipset support
As your problem is only at boot, you could try running sfc /Scanboot.
This will scan all protected system files every time you start your computer. You should revert it back to default settings later using sfc /Revert (details here: Description of Windows XP and Windows Server 2003 System File Checker (Sfc.exe))
Do you turn it off during the day or use standby or hibernate? I wonder if there is anything different in the morning (besides it being cooler, but that is usually a good thing). Having said that, what about your memory? Have you tested it (I suggest Memtest86: www.memtest.com
Let us know