Thanks Giorgio for your advice!
OK, tomorrow I try to uninstall the sql server and install the avast’s sql.
But I am thinking an other idea, it’s possible keep the default instance of sql server 2000 and install avast sql( sql server 2008 r2 express) in an another instance ? the two instances do not conflict between them?
(I have a disk clone with the original configuration with only sql server 2000 without avast and sql server 2008)
bye
Marco