I haven't broken all of these down, but they all have the same (other than the video card error back in December of '09 thrown in) bus error:
Code:
2: kd> !errrec fffffa80085178f8
===============================================================================
Common Platform Error Record @ fffffa80085178f8
-------------------------------------------------------------------------------
Record Id : 01cae36a66f2fa1f
Severity : Fatal (1)
Length : 928
Creator : Microsoft
Notify Type : Machine Check Exception
Timestamp : 4/24/2010 4:55:56
Flags : 0x00000002 PreviousError
===============================================================================
Section 0 : Processor Generic
-------------------------------------------------------------------------------
Descriptor @ fffffa8008517978
Section @ fffffa8008517a50
Offset : 344
Length : 192
Flags : 0x00000001 Primary
Severity : Fatal
Proc. Type : x86/x64
Instr. Set : x64
Error Type : BUS error
Operation : Generic
Flags : 0x00
Level : 0
CPU Version : 0x000000000001067a
Processor ID : 0x0000000000000000
===============================================================================
Section 1 : x86/x64 Processor Specific
-------------------------------------------------------------------------------
Descriptor @ fffffa80085179c0
Section @ fffffa8008517b10
Offset : 536
Length : 128
Flags : 0x00000000
Severity : Fatal
Local APIC Id : 0x0000000000000000
CPU Id : 7a 06 01 00 00 08 04 00 - fd e3 08 0c ff fb eb bf
00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00
Proc. Info 0 @ fffffa8008517b10
===============================================================================
Section 2 : x86/x64 MCA
-------------------------------------------------------------------------------
Descriptor @ fffffa8008517a08
Section @ fffffa8008517b90
Offset : 664
Length : 264
Flags : 0x00000000
Severity : Fatal
Error : BUSL0_SRC_ERR_M_NOTIMEOUT_ERR (Proc 0 Bank 0)
Status : 0xf200084000000800
3: kd> !sysinfo smbios
[SMBIOS Data Tables v2.5]
[DMI Version - 0]
[2.0 Calling Convention - No]
[Table Size - 1337 bytes]
[BIOS Information (Type 0) - Length 24 - Handle 0000h]
Vendor American Megatrends Inc.
BIOS Version P1.60
BIOS Starting Address Segment f000
BIOS Release Date 03/27/2009
BIOS ROM Size 100000
[BaseBoard Information (Type 2) - Length 15 - Handle 0002h]
Manufacturer ASRock
Product P45XE
3: kd> !sysinfo cpuinfo
[CPU Information]
~MHz = REG_DWORD 3113
Component Information = REG_BINARY 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
Configuration Data = REG_FULL_RESOURCE_DESCRIPTOR ff,ff,ff,ff,ff,ff,ff,ff,0,0,0,0,0,0,0,0
Identifier = REG_SZ Intel64 Family 6 Model 23 Stepping 10
ProcessorNameString = REG_SZ Intel(R) Core(TM)2 Quad CPU Q9550 @ 2.83GHz
Update Signature = REG_BINARY 0,0,0,0,7,a,0,0
Update Status = REG_DWORD 6
VendorIdentifier = REG_SZ GenuineIntel
MSR8B = REG_QWORD a0700000000
Processor may be overclocked!
Expected Frequency: 2830
Actual Frequency: 3113
Overclock Ratio: 1.10
It's a BUS interconnect error (specifically a cache miss and timeout gathering data from cache), and it's flag is 0x00 meaning it's a local processor originated request (according to the Intel documentation on the MCA architecture in Intel CPUs). So either it happens because there's some problem with the video card (or bus), or you have a failing CPU under load. I honestly couldn't tell you which, and given you built this system yourself it seems (looks like an ASRock P45XE with an overclocked Q9550 running at 3.1GHz), you might just want to try and remove the overclock to see if things get stable again