On my old XP PC >6 years, avast! 6 really has helped speed up things. I also do not like webrep and on the prompt to install it after re-boot, I simply clicked no.
Uninstall webrep like craigb said, uninstall chrome (if by mistake you clicked the checkbox ok to install it) and disable auto sandboxing or add your normal programs to its allow list.
Even with v6.0.1, my old single core PC is much faster (and I have never done any re-install at all these 6 years) than with v5 or initially with AVG.