One Care backup can be turned off. Open One Care>Change Settings>Backup>Configure Backup>Change Settings> Turn off backup on this computer. One Care backup does not back up the operating system or programs, it only backs up data files. If you have a large amount of videos,photos, music etc. on three computers backup may require a large amount of disc space even though the backups are compressed into zip files.
Support should be able to help you install IE7.