x32 does not exist. You might mean 32-bit. That is x86 (the 32-bits intel family; pentium 4, intel core duo etc.). The other one is x64, and that means 64-bit (64-bit amd family; Athlon 64 etc.). Normally x64 is better, because it uses better calculations that 32-bit. But most applications run best on the 32-bit version of Vista. So for short, 64-bit is faster, but less compatible. 32-bit is slower, but more compatible. If you have a 32-bit motherboard and/or CPU (like a Pentium 4), then you can only run the 32-bit (x86) version of Vista.
If you want to be sure what architecture (x86 or X64) your CPU is, then go to command prompt, and enter echo %processor_architecture% The architecture will now be displayed
