I get this all the time. Here is what you most likely need to know. If you are running Windows XP, it is almost certain that you don’t have 64bit windows installed. With Windows Vista or 7, you can check with a few simple clicks.
Right click on the Computer icon. It should be on your desktop or in the Start Menu. Then left click on Properties. It will open the System window, which will have, as the screenshot above shows, information about your computer, including how much RAM you have and whether you are running 32 or 64-bit Windows.
It is important to note that you may have 32-bit Windows installed on a computer that can handle a 64-bit operating system, but to determine that you may need to run a special program like CPUZ or WCPUID. But almost anything manufactured in the last 5 years ought to do 64-bit computing, with the biggest exception being Intel’s Atom Processor, found mostly in Netbooks.