Your SATA drive will support conventional Molex power source and your MB has native support.
Here is an issue you may have, the original XP only has native support for up to 137gb drives. You have to apply services packs to support the larger drive. If you are installing and old copy of XP, you have a few choices, find and download a SATA driver from Asus if it exists (good luck finding it - the asus web site is horrible), use the utility that comes with the drive to clone your current installation, install on a small partition and use a tool like partition magic to expand your partitionafter you apply your service packs, or you'll need to partition the disk - not the best choice IMHO.