I am using sp3 win xp 32bit and have installed a 3ghz quad core . I have the same motherboard at work (p5n-d asus) and that one is showing 4 cpu's in task manager under proformance tab and show all cores.
My problem is my home comp shows only 2 cores in the window and not 4 cores like my work comp?
Check the device manager under "computer". It should read something like ACPI mutiprocessor PC. if it doesn't, the wrong HAL may be installed. Right click it and select update driver then select the correct HAL.