According to Neowin.net the successor to Windows Live OneCare known as Microsoft Security Essentials (MSE) is due to hit Beta form next week starting on June 23rd.
The free anti-virus / anti-spyware solution will begin with a limited beta and will release an updated build over the Summer. Microsoft is initially targeting the first 75,000 US, Israel and Brazil based customers with a Chinese Beta available in mid-July.
Neowin have also learned that Microsoft is targeting September or at the latest to have the anti-virus software available for the October 22 Windows 7 launch.
Similar to the Windows 7 beta it is likely the company will expand the offering to meet demand.
Below is a screenshot of the MSE Beta.