Help me decide best backup

I use a drive bay and switch out various drives/OS's. I need to come up w/a good backup solution but don't want to spend on software. I have 1 HD 2/3 full using 7 Premium, 1 320GB w/XP and not much else and 1 500GB HD I want to install another 7 on that's empty.

I'm deciding on various free Backup appl versions and don't want to use the internet. I burn data files and media to CD/DVD. Can I create partitions on 2 or all 3 HD's and backup one OS to one of the other HDs' partiton (externally) AND set that B.U. partiton so it can't be accessed when I use it internally (to run another OS)? Encryption, file table, etc.? It would obviously defeat the purpose if a virus could mess up the backup partition.

Also, I'm agreeing w/some who think cloning is best but that would take up a lot of space. Yet all imaging involves compression, right? I'm pretty certain my Ghost and Partition Magic versions aren't compatible w/7. Is there some appl to make the partitions so no virus can see or access it?

I could use the new drive and clone the 7 Premium to it. The Premium HD is 3 yrs old. But I want to load a fresh 7 for some work related appls...
The more I read on Backup appls the better NAS sounds but, you know, money's tight right now.

Hello i am not that much aware with it but still you search about the best backup on Google you will get many site which will explain you this in more details. and in addition if you got any solution for this then please share it with us so we will get some information about it.