I'm trying to install Linux Mint alongside Windows 8 on my laptop, but the install disc did not recognize Windows, so I'll have to do a custom install, which is something I've never done, and I want to back up my Win install in case I screw up and I can't fix it with the boot-repair CD.

On my HDD first I have three hidden Windows partitions, the 2nd one being the boot partition, the C: partition which has Windows and important stuff that I want to back up, then the D: partition which is very large with media files and I don't care much for it, and then some empty space where I would put Linux at the end.