mShred wrote:You can install any OS onto a HDD.
What I'm trying to wrap my head around is why you're trying to go with the pentesting OS's. In my own experienced opinion, it would make more sense to learn how to use linux fluently before you go trying to use a pentesting OS and tools that are generally all ran on a terminal that you wouldn't know how to use.
It makes sense to me. You want to learn everything, and you want to learn it fast, so you dive right in to the middle of everything with a pentesting OS.
It's only when you've done that a couple times that you start to learn that it doesn't work, and there's so much new stuff going on that you can't focus long enough to learn anything, and you finally give up and go do something else.
So mShred's right. Start with learning just Linux. Don't try to learn everything; pick one thing and master that. Once you're comfortable working with Linux, move on to something else. If you bite off more than you can chew and try to go for everything at once, you'll get frustrated. Take it in small, bite-size pieces, and you'll be up and going before you know it.