Can I use the same product key to run a dual boot OS (Windows 7) on a single PC (OEM)

No, the key which can be used with either 32 or 64 bit Windows 7, it is a single install. 1 license, 1 installation, so choose wisely. If you want to install Windows 7 32 or 64 bit on another partition or another computer, you will need to purchase an additional license.

http://www.microsoft.com/windows/buy/default.aspx

http://windows.microsoft.com/en-us/windows7/Get-a-new-Windows-product-key

If you comply with these license terms, you have the rights below for each license you acquire.

1. OVERVIEW.

a. Software. The software includes desktop operating system software. This software does not include Windows Live services. Windows

Live is a service available from Microsoft under a separate agreement.

b. License Model. The software is licensed on a per copy per computer basis. A computer is a physical hardware system with an internal storage device capable of running the software. A hardware partition or blade is considered to be a separate computer.

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.