Just install avast… the Outlook plugin must be enabled.
Outlook 2000 > Tools menu > Options > Other > Advanced Options > Add-In Manager.
Sure, avast protects all emails accounts in MS Outlook, not only the one used for registration. For other email programs (like OE or Thunderbird), just run Mail Protection Wizard.
Yes. http://forum.avast.com/index.php?topic=31426.msg261586#msg261586