You'll need to install either the Windows OEM Preinstallation Kit (Windows OPK) or more likely, the Windows Automated Installation Kit (Windows AIK)
WAIK can be found here:
http://www.microsoft.com/downloads/details.aspx?FamilyID=c7d4bc6d-15f3-4284-9123-679830d629f2&DisplayLang=en
Once you have that downloaded (it's a 1GB .img file) - you can burn it to DVD and install WAIK ((you can rename the ".img" to ".iso" if you're more familiar with that.