Product key for 32bit Vista will not work with 64bit. also the product key you have will also not work with the retail version DVD even if it is 32bit. because your product key is of Volume licensing and the version you have on your DVD is OEM version of Windows. (There is a separate product key for 32bit and 64bit OEM version) I would suggest you to either go with Windows 8 64 bit or Windows 7 64 bit (if you are not ready for Metro UI). That $40 is worth spending over Vista's resource hungriness and driver issues (specially since you have Dell, Dell is very well known for it's laziness for supporting older systems and older OS).