I think you may be missing a number off your motherboard. Could it possibly be a 6178?
You will find it listed on Crucial under MSI.
Almost certainly, your motherboard will NOT support DDR memory. This is a later version of SDR which I suspect is what your looking for.
But first, ask yourself why you want to change to XP.
Although there is no question it will run on your machine, it will be considerably slower than '98. Arguably, it's more stable, but are you suffering from instability? There will possibly be incompatibility problems with hardware, and almost certainly with drivers. As I have said before here, it is not the panacea that Microsoft would have you believe!