Just saying, despite the technology used in SSDs, the correct term for the 'room' taken up by a Windows installation is 'disk space', not 'memory'. That's something different. Having got that out of the way, my Windows 7 Professional 64-bit install, just over a year ago, into a 100 GB system partition, was about 12 GB at first, before I installed any programs, and copied my documents, pictures, etc from my older computer, but it now takes up 46 GB, so I would allow a serious amount of headroom in a real world setup. Like the others, I don't think the expense would be worth it.