OneCare does not backup the whole PC. it only backs up data, selected by configuring the backup plan in OneCare. You choose the file types to be backed up and where to backup to. Note that you cannot backup any files from \Windows or \Program Files and there are a number of file types that will never be backed up by OneCare. This article contains the list:
http://support.microsoft.com/default.aspx/kb/943776/en-us
In the event of a drive failure or other need to restore your data, you would reinstall Windows to a new drive or after a wipe of the drive, then install OneCare, then use the restore wizard to restore your data.
When you perform the first backup, it is a *full* backup of all data matching your plan. Subsequent backups will only be for new or changed files.
OneCare will backup data to an external USB drive, CD/DVD, some flash media (thumb drives), or a network Share. it cannot use an internal drive for the backup destination without using an unsupported workaround (explanation pinned to the top of this forum topic folder).
If you wish to perform a full image based backup and bare metal recovery, meaning your backup returns your PC to the state of the last backup - all files, programs, settings, etc., you will need to get a different program. One that I have used in the past is Acronis True Image. www.acronis.com
-steve
Microsoft MVP Windows Live / Windows Live OneCare Forum Moderator
