Use the cleanup tool -
http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=828910&SiteID=2
Then install from http://onecare.live.com and activate with a LiveiD and the PIN from one box on the first PC and then the same LiveID on the second PC. Hold onto the second box (and retail key) for renewal as you are allowed to have up to 3 computers running one subscription of OneCare. Two boxes = two subscrptions.
You didn't actually need to remove OneCare, either, unless you were using the beta. The trial and subscriber copies are identical, the difference being the activation of the subscription.
If the above doesn't work, providing the error or errors you are encountering might help in providing more help.
See this post for the KB article to troubleshoot install problems - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=1588602&SiteID=2
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve
