brute force is guessing until you get it right, usually how you decrypt password files, unless there was some flaw in their encoding.
Theres quite a bit of risk in trying to hack other people, your best bet is to try and setup 2 boxes.1 with a variety of OS's and another one running some sort of Unix OS.
You might also want to try VMware (lets you create virtual machines inside your own).
I'm not too sure how well that'll work for laerning to hack, but if the second box isn't available it's a good avenue to try.