WinXP crashes in random intervals (with minidump output)

I found some more info on STOP 0x7f.  It is written for Win2000, but it presumably also applies to XP:

http://www.microsoft.com/technet/treeview/default.asp?url=/technet/prodtechnol/windows2000serv/reskit/serverop/part4/sopch16.asp

Stop 0x0000007F or UNEXPECTED_KERNEL_MODE_TRAP
This Stop message, also known as Stop 0x7F, means that one of two types of problems occurred in kernel-mode, either a kind of condition that the kernel is not allowed to have or catch (a bound trap), or a kind of error that is always fatal. Occasionally, this message can be caused by software problems, but the most common cause is hardware failure.

Interpreting the Message
The four parameters listed in the message are defined in order of appearance as follows:

Processor exception code
0 (zero)
0 (zero)
0 (zero)
The first and most important parameter (0x0000000x) can have several different values. The cause of this error can vary, depending on the value of this parameter. All conditions that cause a Stop 0x7F can be found in any x86 microprocessor reference manual because they are specific to the x86 platform. Here are some of the most common exception codes:

0x00000000, or Divide by Zero Error, is caused when a DIV instruction is run and the divisor is 0. Memory corruption, other hardware problems, or software failures can cause this error.
0x00000004, or Overflow, occurs when the processor executes a call to an interrupt handler when the overflow (OF) flag is set.
0x00000005, or Bounds Check Fault, is generated when the processor, while executing a BOUND instruction, finds that a variable's assigned value exceeds the specified limits. A BOUND instruction is used to ensure that a signed array index is within a certain range.
0x00000006, or Invalid Opcode, is generated when the processor attempts to run an invalid instruction. This is generally caused when the instruction pointer has become corrupted and is pointing to the wrong location. The most common cause of this is hardware memory corruption.
0x00000008, or Double Fault, is when an exception occurs while trying to call the handler for a prior exception. Normally, the two exceptions can be handled serially. However, there are several exceptions that cannot be handled serially, and in this situation the processor signals a double fault. This is almost always caused by hardware problems.
Other exception codes are defined as follows:

0x00000001—A system-debugger call.
0x00000003—A debugger breakpoint.
0x00000007—A hardware coprocessor instruction with no coprocessor present.
0x0000000A—A corrupted Task State Segment.
0x0000000B—An access to a memory segment that was not present.
0x0000000C—An access to memory beyond the limits of a stack.
0x0000000D—An exception not covered by some other exception; a protection fault that pertains to access violations for applications.
Resolving the Problem
Hardware failure or incompatibility. Stop 0x7F usually occurs after the installation of faulty or mismatched hardware (especially memory) or in the event that installed hardware fails. If hardware was recently added to the system, remove it to see if the error recurs. If existing hardware has failed, remove or replace the faulty component. Run hardware diagnostics supplied by the system manufacturer, especially the memory scanner, to determine which hardware component has failed. For details on these procedures, see the owner's manual for your computer. Check that all the adapter cards in the computer, including memory modules, are properly seated. Use an ink eraser or an electrical contact treatment, available at electronics supply stores, to ensure adapter card contacts are clean. Be sure to wipe the cleaned contacts off, removing all cleaning debris, before reinstalling the adapter card into the computer. If compressed air is available, use it to clear out the adapter card slot.

If the error appears on a newly installed system, check the availability of updates for BIOS revisions on the motherboard, SCSI controllers, or network cards. Updates of this kind are typically available on the Web site or BBS of the hardware manufacturer.

Confirm that all hard disks, hard disk controllers, and SCSI adapters are listed on the Windows 2000 Hardware Compatibility List (HCL). For more information about the HCL, see "Additional Resources" at the end of this chapter.

If the error occurred after the installation of a new or updated device driver, the driver should be removed or replaced. If, under this circumstance, the error occurs during the startup sequence, restart the computer using Safe Mode to rename or delete the file. If the driver is used as part of the system startup process in Safe Mode, you need to start the computer using the Recovery Console in order to access the file. For more information about Safe Mode, see chapter "Startup Process" in this book. For more information about the Recovery Console, see chapter "Repair, Recovery, and Restore" in this book.

Also try restarting your computer, and press F8 at the character-mode screen that displays the prompt "For troubleshooting and advanced startup options for Windows 2000, press F8." At the resulting Windows 2000 Advanced Options menu, choose the Last Known Good Configuration option. This option is most effective when only one driver or service is added at a time.

Overclocking. Setting the CPU to run at speeds above the rated specification (known as overclocking the CPU) can cause this error. If this has been done to the computer experiencing the error, return the CPU to the default clock speed setting.

Check the System Log in Event Viewer for additional error messages that might help pinpoint the device or driver that is causing the error. Disabling memory caching of the BIOS might also resolve it.

If you encountered this error while upgrading to Windows 2000, it might be caused by a device driver, a system service, a virus scanner, or a backup tool that is incompatible with the new version. If possible, remove all third-party device drivers and system services and disable any virus scanners prior to upgrading. Contact the software manufacturer to obtain updates of these tools.

Microsoft periodically releases a package of product improvements and problem resolutions for Windows 2000 called a Service Pack. Because many problems are resolved by installing the latest Service Pack, it is recommended that all users install them as they become available. To check which Service Pack, if any, is installed on your system, click Start, click Run, type winver, and then press ENTER. The About Windows 2000 dialog box displays the Windows version number and the version number of the Service Pack, if one has been installed.

Occasionally, remedies to specific problems are developed after the release of a Service Pack. These remedies are called hotfixes. Microsoft does not recommend that you install a post-Service Pack hotfix unless the specific problem it addresses has been encountered. Service Packs include all of the hotfixes released since the release of the previous Service Pack. The status of hotfix installations is not indicated in the About Windows 2000 dialog box. For more information about Service Packs and hotfixes, see "Additional Resources" at the end of this chapter.

Finally, if all the above steps fail to resolve the error, take the system motherboard to a repair facility for diagnostic testing. A crack, a scratched trace, or a defective component on the motherboard can also cause this error.

For more troubleshooting information about the 0x7F Stop message, refer to the Microsoft Knowledge Base link , using the keywords winnt and 0x0000007F. For information about this resource, see "Additional Resources" at the end of this chapter.