That should work just fine.
The way the 64 bit processors work is that they are 32 bit processors that have extra capabilities for 64 bit, so they can be told to run as a 32 bit processor or a 64 bit processor. If the processor is told to run as a 32 bit pocessor it cannot run 64 bit applications. If it is told to run asa 64 bit processor it can also run 64 and 32 bit applicaiton. Your operating system, Windows XP in your case, tells the processor when Windows XP boots to run as a 32 bit processor.
Power stations. Is there a rule of thumb on if you want a 450w or 850w?
Tom's Hardware has a formula but it looks extremely detailed. Is too much power bad?