Building Your Own Computer

I am looking into building my own computer with accontants as my target users.
Requirements
??? Small form factor solutions (no full size ATX towers)
??? On-board video with DVI or HDMI interface
??? On-board LAN (10/100/1000 Ethernet); wireless not desirable
??? Must be capable of running Windows 7 Enterprise
??? Local Storage only needs to be large enough for OS and installed software
What would be the absolute minimum amount of parts I would need to build this computer while being cost efficient. The less money spent on parts not needed can be put towards better parts for better performance.
Pls respond with your opinions for possible solutions