If you originally activated your OneCare subscription with a retail key, then there's no reason to cancel, since it will simply expire. If you have a credit card on file and it is being renewed automatically, you will want to cancel the OneCare subscription and obtain a refund if you were charged. You will need to contact support to do this.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
When you are ready to install Equipt, you will want to uninstall OneCare first so that the Equipt with OneCare subscription would take effect for the entire suite.
If you have a copy of Outlook already running, Equipt will not touch the Outlook license and it remains. If you have any of the other Office programs that come with Equipt, you probably want to uninstall them first.
-steve