It doesn't matter which service pack you install, what matters is which service pack you are running at the momment you create the partition, right at the beginning of your install process. Installing SP3 afterwards won't solve your problem, using at first an install disc that has SP1 or later included (slipstreamed) will. Now you are left with the 2 options I listed above. A 3rd option is to create a slipstream disc and reinstall your XP but that would take you much more time. Creating a 2nd partition (that would translate in a D: drive) is by far the best option.