I am using Windows 2000 SP4 and had no problem using avast PRO ANTIVIRUS.
Since November 2012 I have the following entry in the event viewer:
Event ID 7026, Source: Service Control Manager, aswSP could not be loaded.
Version Info c:\WINNT\system32\drivers\aswSP.sys 7.0.1474.765
avast PRO is Version 7.0.1474