The backups are in standard zip files, that can be opened by Windows Explorer and can also be opened by Winzip and other 3rd party compressing/archive programs. However, if any file within these zip files has been split by OneCare during the backup due to being large, you'll need to extract the parts and re-join them using a 3rd party utility such as this one -
http://www.freebyte.com/hjsplit/
-steve