Some other questions - we need some more information to help you:
...so I expanded a new copy.
- You'll need to explain that. Do you mean you extracted a copy from the Windows XP CD? If so, was the CD an SP1 CD or a pre-SP1 CD? You can't mix file versions.
- When and under what circumstances did you get the pci.sys error? Did you update a driver?
- When are you getting this stop code, at boot?
- Can you boot into Windows desktop at all?
- Can you boot into Safe Mode?
- Does the computer reboot by itself after this error?
07E errors are generally related to driver issues. If you just installed a new driver then it's likely that driver is corrupt, the wrong driver, or conflicting with something else. It could also be the device has failed.
If the driver was for a device that can be removed (like a card or a USB device), disconnect it.
If it was your video card you'll need to roll back the driver. You should be able to get into Safe Mode. Failing that, select "Use last known good configuration.." from the boot menu.
If you can at least get into Safe Mode then you can use System Restore to restore the computer to a restore point prior to when this happened. NOTE: Do not pick the day before! Go back at least a week before. Due to the way System Restore works, going back a day may not fix the problem.
Hope this helps...