Take a look at this post -
http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=1848280&SiteID=2
Basically, there is no impact. You will need to remove OneCare 1.6 if you wish to try the beta. Your subscription will continue to exist, but it won't apply to the beta. It will not extend the subscription period and you will need to uninstall the beta and reinstall the subscriber copy and activate with your subscription LiveID once again at the end of the beta.
-steve