I too have a similar problem AvastSvc has high CPU usage and 100MB mem usage when scanning .exe files. I keep the setup of all programs i use.If I ever open that folder or the downloads folder everything freezes until avast has scanned the files.I cant even open avast to see which files are been scanned.
Strangely I only have this problem in Windows XP SP3, not in Windows7.
I have both OS installed on same PC.
Hi guys and welcome to the forum…! 
You better start new threads to get more attention… 
asyn