If you are interested in a third option:

I would use a gaprted live CD (http://gparted.org/download.php) and shrink the existing partion(s). Now you could run a standard Windows Installation and use the free disc space for your NTFS partition. After the Windows Installation, your bootloader won't start, so you have to repair it using a linux live CD (http://http://en.opensuse.org/SDB:Repair_MBR_after_Windows_install).
This will also work.