My system is WinXP Home/SP3/ with avast! free 5.1.889.
I, too, have disabled rootkit scan and my high CPU activity (was running 90+% avastsvc.exe regularly) has ceased - after reboot. I am using Cobian backup software version 9, but that didn't seem to matter in Heldon's case. I have Spybot-S&D 1.6.2 resident, also.
One other interesting note: My screen saver now works properly, whereas before the rootkit scan disable it did not.
Thanks.