Assuming you've got the drive plugged in etc -
Put the XP CD in
Go into the BIOS and make sure boot from CD is before boot from HD
Save and exit the BIOS
Follow the instructions to boot from the CD
Follow the instructions in the Windows setup
Create 2 partitions using NTFS (Quick), one 200GB, the other using the remaining space (~440GB)
Continue to follow the instructions
You can't go too far wrong really. If you have an XP Service Pack 2 or better CD it'll be straightforward. If not, you *may* have to install SATA drivers for your motherboard. You may have been given a floppy disc with your motherboard with the drivers on, or you may have to download them and put them on one. You then need to press F6 when prompted during setup. Hopefully you won't have to bother with this though.