I don't recommend using old hard disks as they do have a life span. I tend to switch mine out every 3 years. But yes, you could use it in a pinch. You will need to do a fresh install of Windows because it is a new system.
Thank you for your help, so i can use the old HP HDD although it's HP OEM for my new comp. Another question is that once windows 8 system builder is installed to the old HDD, does the windows 8 license get stuck with the old HDD? or can i just uninstall windows 8 from the old HDD and then install it to the new HDD that im going to receive soon?