32 bit Build - This is built with the SSE instruction set. If you do not know what your specific processor has for instructions, I HIGHLY recommend that you run a processor utility like the one found here that will tell you exactly what information you need to know.
64 bit Build - Obviously this is meant for users with not only 64 but hardware, but with a 64 bit operating system. If you don't know what this is, please download one of the above.
There are other downloads offered on this site. Please use the links at the top to find the specific one you require.