I don't know if you have solved your problem but I just thought I'll let you know the following fact. In the 'Backup and Restore' window, there's a button called 'Manage Space'. In that, when you click 'Change settings' in the System image section, you have the option of keeping only the latest system image or let Win7 handle it for you. I myself have never let Win7 do so and only keep the latest SysImg and so am not exactly sure this is what you are looking for. If it's not, sorry and good luck. If it is, you're welcome !