Sometimes, AVG 8 will fail to install, giving an error message stating that the AVG 8 Watchdog service has failed to start. In these cases, remove the all-users AVG agent config folder, reboot, and reinstall.
Under XP, this folder is here:
C:\Documents and Settings\All Users\Application Data\avg8\Cfg
Under Vista, this folder is here:
C:\ProgramData\avg8\Cfg