If you have a CPU that can do GPU tasks as well (Sandy Bridge, Fusion) you don't need a graphics card, else you will. Your current motherboard might have a built in GPU.
RAM can be reduced to one stick.
Drives are best replaced with 'green' versions that some manufacturers use, though drives don't use thát much power. Also set your drives to power off after 10 minutes of inactivity.
You should change the energy management to high performance, but turn off automatic sleep mode and enable the automatic downclocking of the CPU. There's also a setting for the minimum CPU frequency, set this to 5%.
A screen is only necessary during the installation of Windows, you can access it through remote desktop on another Windows PC after the installation.
The DVD reader/writer can also be taken out after the Windows Installation. You can use DVD emulation instead.
I'm not sure if the wattage of the PSU makes a difference, but I would downgrade to the minimum needed. Though I need confirmation on this one.
If you need further explanation on anything, let me know.