If i am not mistaken on this. mobo's can only handle a certain speed. So if you put int the P3 where the P@ was it wont work. The speed of the P3 is greater and therefor wont work in the mobo which in turn could damage both the CPU and the mobo.
Also if i am not mistaken P2 and P3 mobos are not compatable with wach other. The P3 had higher specs for FSB and cache. The mobo might not be able to handle it.
I know this is true with newer mobos. I was gonna flip out a Celeron with a P4 but it wouldnt work. They were the same pin but the mobo oculdnt handle the speed. This is going off memory from A+ class so i could be off.
Also if this is to get around the problem you are having with your XP install 2Fast this still wont work. XP will not recognize the hardware installed. The processor will be the same but the rest of the hardware you have installed will still give you the stop 7b error.