Depends on your processor. I am assumeing that you do not have one of the new Intel or AMD 64-bit processors, so you should use the IA-32 version.
You should make sure of what processor you have before you do this, just to be safe. I am also assumeing that you would know if you had a 64-bit processor because, at this point, you'd really have to go out looking specifically for one of these to get one.....