The LiveID used by OneCare really has nothing to do with the email account origiinally used to create it, it's simply named the same. I've got exactly this same situation with an account I use to protect the PC for another member of my family, since we've switched ISPs from Dial-up to Broadband.
Since that OneCare subscription will be up for renewal in April 2009, I will be creating a new LiveID account shortly before that occurs and then uninstall and reinstall OneCare using that new account. Because the old account will attempt to auto-renew, I will also need to cancel that account before it comes due, which isn't necessary if the account was never given Credit Card information.
There's also a tool available that can reset the associated subscription so you don't have to uninstall/reinstall. It's listed in the Instant Help for Windows Live ID under "Reset a Windows Live ID or fix a greyed-out Windows Live ID".
To insure you receive notification of that other account's renewal status, log into it at http://billing.microsoft.com/ and change the notification email address under Personal information to one you currently use.
OneCareBear
