The product key for OEM copies of Windows only work with the version ordered with the computer. If you order the computer with a 32bit W7 Pro that is all you will be entitled to and the product key will not work with anything else but W7
Order the computer with a 64bit copy of Pro or buy a retail upgrade copy of Windows 7 Pro after the fact. Retail copies come with both versions and a product key that can be used with either. Although a custom installation is required when
changing versions, the upgrade license is fine for doing so.
You can use a retail Windows 7 dvd on any computer but you need copies of Windows for each because each installation requires its own product key. This is from a Windows 7 retail license.
2.INSTALLATION AND USE RIGHTS.
a.One Copy per Computer. You may install one copy of the software on one computer. That computer is the “licensed computer.”
b.Licensed Computer. You may use the software on up to two processors on the licensed computer at one time. Unless otherwise provided in these license terms, you may not use
the software on any other computer.
c.Number of Users. Unless otherwise provided in these license terms, only one user may use the software at a time.
d.Alternative Versions. The software may include more than one version, such as 32-bit and 64-bit. You may install and use only one version at one time.
I suggest you not order the computer with the 32bit version. Save some money and buy it with the 64bit version in the first place.
Colin Barnhorst Windows 7 Ultimate x64 on DIY with 6GB ram.