How to get a 64 bit computer?

It does not matter what your CPU has. The GPU on the graphics card will work regardless. All Pentium 4s up to and including the Prescott core are 32-bit only. The Cedar Mill core is 64-bit capable, but it is used mainly in lower-end systems with 32-bit operating systems. All AMD CPUs you buy today are 64 bits. You also need to use a 64bit OS such as Linux or Windows 7. BUt as I said, the graphics card's GPU will work independently.