Hi,
I think the problem is that what we use to detect the number of processors on XP perhaps doesn't tell us the correct number of cores, only the number of actual processors. So, for a machine which has 2 processors but 4 cores, it will only tell us that there are two processors available. It will also give different results if your processor(s) use HyperThreading. For Server 2003 up, including Vista, we do it another way which is accurate. There is another way to do it on XP but it is much more complicated.
Regards,
Jo