I'm planning an upgrade..new MB and CPU and reformatting an older hard drive which is the one with Windows XP on it. Would it be better to reformat in advance, or after install? JamesJ

I'd change the hardware and then let XP do the reformat during the OS installTrip

But will windows have to be reinstalled after changing the mb and processor? Seem to me it would already be there..JamesJ

If you just change the mobo and CPU, WinXP will still be there on the HDD and it won't have be reinstalled (but it will probably have to be reactivated). But if, as you said in the original post, you format the drive then WinXP will have to be reinstalled.Trip(Edited 'cause I can't spell!)

James & Trip,This may only be my recommendation, but your existing Windows installation was for your old motherboard & system configuration. Specific drivers and registry entries are for the old system, not the new motherboard, chipset, etc.You can certainly try the 'upgrade', but if it were me, I'd backup any information that you deem necessary and start from scratch.Either way, have fun with the new system and Happy Holidays.