Hi, your CPU is already 64 bit enabled, and i am pretty sure (even without knoweing the model) your motherboard will be too.
Your processor supports 64-bit operating systems as it has Intel(R) Extended Memory 64 Technology.
Now to upgrade your processor, the only people that can tell you which processors are supported is the system manufacturer as the chipset may be compatible with it but if the BIOS does not know how to use it then your system wont boot or it wont work correctly.
Your processor supports a 64-bit operating system, but whether or not you should upgrade to 64-bit vista depends more on the amount of RAM you want to utalize. If you have more than 3.5 GB of RAM then it would be wise to upgrade, if you have less then stick with 32-bit to get the fastest speeds out of your system. Personally, I would not ugrade to a 64-bit system unless I was using more than 4GB of RAM, due to the cost of the operating system versus what you will actually get outof it.