is MY copy of Windows XP Pro 32-bit?

Question

I've got a 32-bit machine (Pentium 4) running Windows XP Pro (version 2002). I understand that there are 32- and 64-bit versions of Windows XP Pro, and that some 64-bit versions of XP Pro will run on 32-bit machines (although I can hardly believe it, and I've also been told that's not true). So how do I know for sure that my copy of XP Pro is 32-bit?