Everyone who have read the earlier posts Download a Legal Beta Copy of Windows 7 beta ( 32 bit or 64 bit ) on January 9th and Get the Windows 7 beta product keys for activation would have been playing with Windows 7. The next thing your OS requires is an antivirus to keep you protected.
Kaspersky is offering a free technical preview of it’s Kaspersky Anti-Virus for Windows 7. This is valid for 5 months. Download it from here.
Norton 360 Version 3.0 Beta is also available for 90 days. Download it from here.
If you finish the above trials, can always try Avast! Home Edition free.