I'm building a new pc for my grandparents in order to replace their current computer that is god awfully slow at times. I'm going to re-use their HDD, but I was wondering if this would work? This HDD has Windows 7 loaded on it, so I figured that in order to save them the expense of buying a new hard drive and OS, I would just install the hard drive into the new pc I build them. Will this work or do they need a new copy of Windows 7? Would they also need a new HDD? Their copy of Windows 7 is a System Builder edition.