Windows xp & registry key problem

The question I have is: Although I get the following error:
Local machine: installation failed
Installation:
Error: Action failed for registry key HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows: creating registry key....
Error 0x80070005

...Can I just download a different antivirus software BESIDES AVG and eliminate the whole registry key problem......or is it there to stay until addressed? I've tried to run 'regedit', as instructed on this forum with full permission......

Do I need to uninstall and reinstall my windows xp service pack???
Thank you for your patience......