ATI HD 4850 Drivers not Supported or Not Installed!

I have a 24" iMac with ATI HD 4850 Graphics Card. I am running Windows Vista on Boot Camp.
I recently installed Vista Service Pack 1, then when I restarted my computer, Vista started with a resolution of 1600x1200 and an ATI error message saying

Also when I go to my device manager I see that Standard VGA Graphics Adapter cannot start. (Code 10).

I tried reinstalling the video drivers twice from 2 different sources (my Drivers DVD that came with my mac and AMD/ATI's website) and I even uninstalled Service Pack 1. And still I have the same problem.

My resolution used to be 1920x1200 and now it's only 1600x1200, which is low for a 24" screen. And now I can't play any games either

Here is my DxDiag Results, you can see that Vista can't even tell what kind of graphics card I'm using!

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System Information
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Time of this report: 5/24/2009, 12:19:27
Machine name: MOZER-PC
Operating System: Windows Vista™ Business (6.0, Build 6001) Service Pack 1 (6001.vistasp1_gdr.090302-1506)
Language: English (Regional Setting: English)
System Manufacturer: Apple Inc.
System Model: iMac9,1
BIOS: Default System BIOS
Processor: Intel(R) Core(TM)2 Duo CPU E8335 @ 2.93GHz (2 CPUs), ~2.9GHz
Memory: 3046MB RAM
Page File: 949MB used, 5344MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 10
DX Setup Parameters: Not found
DxDiag Version: 6.00.6001.18000 32bit Unicode

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DxDiag Notes
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Display Tab 1: No problems found.
Sound Tab 1: No problems found.
Input Tab: No problems found.

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DirectX Debug Levels
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Direct3D: 0/4 (retail)
DirectDraw: 0/4 (retail)
DirectInput: 0/5 (retail)
DirectMusic: 0/5 (retail)
DirectPlay: 0/9 (retail)
DirectSound: 0/5 (retail)
DirectShow: 0/6 (retail)

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Display Devices
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Card name:
Manufacturer:
Chip type:
DAC type:
Device Key: Enum\
Display Memory: n/a
Dedicated Memory: n/a
Shared Memory: n/a
Current Mode: 1600 x 1200 (32 bit) (1Hz)
Monitor:
Driver Name:
Driver Version: ()
DDI Version: unknown
Driver Attributes: Final Retail
Driver Date/Size: , 0 bytes
WHQL Logo'd: n/a
WHQL Date Stamp: n/a
Device Identifier: {D7B70EE0-4340-11CF-E025-7137AFC2CB35}
Vendor ID: 0x0000
Device ID: 0x0000
SubSys ID: 0x00000000
Revision ID: 0x0000
Revision ID: 0x0000
Video Accel:
Deinterlace Caps: n/a
DDraw Status: Not Available
D3D Status: Not Available
AGP Status: Not Available

Any help or information would be deeply appreciated.