I currently have Windows 7 Home premium 32bit on my laptop which i upgraded over Vista 32bit. If i buy Windows 7 Ultimate full retail version can i install this over my current OS with the 64bit version?? If not i will just buy another hard drive and do a fresh install. Incidentally, the laptop will work with 64bit. BTW my current hard drive is one i bought separate so i could keep the original laptop hard drive to one side should i ever wish to put it back in. Thanks.