installation - How do I create a partition in order to dual boot Win7?

I just got a new laptop from a friend and I'm decent with computers, however, I am a HUGE noob when it comes to Linux OS (besides backtrack (; ). I downloaded gparted, but there is no way that I am able to create a partition as they are all mounted and in use. Will I need to back up everything on this HDD and then wipe it in order to make a partition to dual boot Windows? I'd rather not go through all that trouble. I have a valid copy of Win7 Ultimate and I'd really like to have a nice laptop with a couple of decent OSes on it. Please help!!