I wanted to temporarily install AVG Antivirus to run a root kit scan. Turned off his McAfee and shut down SpySweeper.

AVG would not install. Complained it could not update the registry key .../Windows NT/Windows. Checked it with Regedit and sure enough - "You don't have pemission". Well, I could get in and with a couple tries at adding "Administrators" to the blank permissions box it'd free up and show all the normal permissions and let me in. If I exited regedit and tried to install AVG it would be locked again.

Found that if I stayed in regedit and held the Windows key open with it, AVG would install just fine. Same thing on uninstall.

. . do a clean install. But it's an HP. It has a Windows license number on the sticker, and another I recovered from Windows itself. No, they don't match, and I know from experience that neither one will activate with Microsoft. They don't give you the 30 days either - they want it NOW! I don't have an HP Windows CD for the Vectra series and the client didn't get one when he bought the PC (used).

No, the root kit scan found nothing. There were some minor infections which had been removed by previous scans with other products.