A repair of the installation should work (Control Panel -> Add/Remove Programs -> avast! antivirus -> Repair).
Anyway, to be honest, I doubt the problems you're seeing are related to the driver.
We will have this driver in the next 4.8 beta refresh (due tomorrow), so we will so what the general acceptance will be like, but I'd be very much surprised if it were causing any problems... the changes were quite "benign", so to say...
Cheers
Vlk