Does Your CPU Support 64Bit? Since some CPU's such as Athlon 64, Athlon X2, Phenom, Athlon 64, Turion, Intel Core 2 64bit is supported.Even some celeron CPU’s and some Pentium Cpu’s support 64Bit.
You can use CPU-Z to understand an existing computer whether capable to 64 Bit. This tiny program shows us all details of proecessor.
Here is compatible with 64-bit EM64T and AMD64 processor can understand if you see phrases. If you are unsure about your processor will need to research.