Ati radeon hd 4800 series crashing my system while playing skyrim

Thought it might be overheating but i downloaded SPeedFan and everything appears to be in hardware limitations...

here are my specs i grabbed from a CoH helper..

DxDiag gathered at January 23, 2012 18:19 (-05:00)
Operating System: Windows Vista™ Home Premium (6.0, Build 6002) Service Pack 2 (6002.vistasp2_gdr.110617-0336)
System Manufacturer: Dell Inc
System Model: XPS 630i
BIOS: Phoenix - AwardBIOS v6.00PG
Central Processor: Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz (4 CPUs), ~2.4GHz
Memory: 8188MB
.Net Memory Report: 6058MB out of 8188MB available
Page File: 13604MB (2983MB currently in use)
C Drive: (NVIDIA STRIPE 931.52G) 791063MB out of 951767MB (83%) free
D Drive: (NVIDIA STRIPE 931.52G) 1024MB out of 2047MB (50%) free
E Drive: (PBDS CDRWDVD DH-48C2S SCSI CdRom Device) zero-size drive
F Drive: (HL-DT-ST DVD+-RW GH30N SCSI CdRom Device) zero-size drive
Windows directory location: C:\Windows
DirectX: DirectX 11
DirectX Diag version: 7.00.6002.18107 (64-bit version)

Display Notes: No problems found.
Sound Notes: No problems found.

No problems found.

No problems found.

No problems found.

No problems found.
Input Notes: No problems found.

Monitor: LG L227W (Digital)
Monitor's Max Resolution: (blank)
Video Device Name: ATI Radeon HD 4800 Series
Manufacturer / Chip: Advanced Micro Devices, Inc. / ATI display adapter (0x9442)
Video Memory: 743 MB
Driver Version: 8.17.0010.1094
Driver Date: 9/8/2011 12:32:58 PM
Driver Language: English

Sound Device Description: Speakers (Realtek High Definition Audio)
Driver File: RTKVHD64.sys
Driver Version: 6.00.0001.5667
Driver Date: 8/18/2008 3:05:28 AM

Sound Device Description: Realtek HDMI Output (Realtek High Definition Audio)
Driver File: RTKVHD64.sys
Driver Version: 6.00.0001.5667
Driver Date: 8/18/2008 3:05:28 AM

Sound Device Description: Realtek Digital Output (Realtek High Definition Audio)
Driver File: RTKVHD64.sys
Driver Version: 6.00.0001.5667
Driver Date: 8/18/2008 3:05:28 AM

Sound Device Description: Digital Output Device (HDMI) (2- High Definition Audio Device)
Driver File: HdAudio.sys
Driver Version: 6.00.6002.18005
Driver Date: 4/11/2009 12:39:51 AM

Sound Device Description: Digital Output Device (HDMI) (High Definition Audio Device)
Driver File: HdAudio.sys
Driver Version: 6.00.6002.18005
Driver Date: 4/11/2009 12:39:51 AM


WMI Information
Motherboard Manufacturer: Dell Inc
Motherboard Model: (empty)
Motherboard Product: 0PP150
Motherboard Version: A00
BIOS Manufacturer: Dell Inc.
BIOS Name: Phoenix - AwardBIOS v6.00PG
BIOS Version: DELL - 42302e31
BIOS Release: 20080715000000.000000+000