Thanks for your reply Parrotmath, but I don't have folder called 'System and Security' in my control panel. I only have a 'system' and 'Security Center.'
A glance through my motherboard manual, under CPU, lists the AMD Athlon 64 processor (K8). I always assumed that that meant that my Athlon 64 was running 64 bit.
Do you know the version of Windows you are running? It's apparently not Windows 7.
Your processor is 64 bit capable, but that doesn't mean you're automatically running 64 bit. That requires you to have both a 64 bit CPU (that you have) and a 64 bit operating system. It seems you probably don't have the latter.