Finally, Microsoft has released a free Antivirus and Antispyware Suite. It is running on my notebook with Windows Vista and I am quite confident. Actually, it has replaced the Security Suite I had been using until now.
The Suite can be downloaded for free at:
BTW, I just learned, that installing Windows Security Essentials will either disable (Vista/Win7) or remove (XP) Windows Defender. Defender is no longer required, because it is being replaced by WSE. However, you really should check if Defender is really disabled/removed. If not, do it.